Why do I keep getting an empty alert box?

I have been working on this for a month now as an exercise and I am still having problems. Every time I get a user to fully validate all information I keep getting an empty alert box. Why is it showing up empty and not with a total amount? Im 95% sure my code is correct: This is my code:

<html>
<head>
<script language="javascript" type="text/javascript">
    
    //function to show province
    function checkProvince()
    {
        var myForm = document.pizzaForm;    
        if (myForm.province.value == "Nunavut" || myForm.province.value == "Yukon")
            {
                alert("We are sorry but we do not deliver here.");
            }
    }
    
    //main function to validate all errors
    function checkName()
    {
        //variable for the alert box to show all errors
        var errMessage = " ";
        //variable to shorten form tag
        var myForm = document.pizzaForm;
        //variable to validate phone number
        var rePhone = /^\(?(\d{3})\)?[\.\-\/\s]?(\d{3})[\.\-\/\s]?(\d{4})$/ ;
        //variable to validate postal code
        var rePostal = /^[A-Z][0-9][A-Z][0-9][A-Z][0-9]$/;
        //validate email
        //var reEmail = /^\D+\@\D+\.\D+$/;
        //variable to shorten telephone tag
        var validPhone = document.pizzaForm.telephone;
        //variable to shorten postalcode tag
        var validPostal = document.pizzaForm.postalCode;
        //variable to shorten pizza number value tag
        var pizzaAmount = document.pizzaForm.pizzaNumber.value
        //var validEmail = document.pizzaForm.email;
        //variable to add the final amount of the order
        var sum = finalAmount + toppingAmount;
        //variable to store final order amount as a string
        var summ = "";
        //variable to show the cost of the pizza times the number ordered
        var finalAmount = "";
        //variable to store the total cost or all toppings
        var toppingAmount = "";
        //summ now holds the final order and converts to a string
        summ = sum.toString();
        
        //validate all form fields
        if (myForm.firstName.value == "" || myForm.lastName.value == "")
            {
                errMessage += "Please type in your name\n";
            }
            if (myForm.address.value == "")
            {
                errMessage += "Please type in your address\n";
            }
            if (myForm.city.value == "") 
            {
                errMessage += "Please type in your city\n";
            }
            if (myForm.postalCode.value == "")
            {
                errMessage += "Please type in your postal code\n";    
            }
            if (myForm.province.value == "")
            {
                errMessage += "Please select a province\n";
            }
            if (myForm.telephone.value == "")
            {
                errMessage += "Please type in a phone number\n";
            }
            if (myForm.email.value == "")
            {
                errMessage += "Please type in your email\n";
            }

            if (!rePhone.test(validPhone.value))
            {
                errMessage += "Please type in a valid phone number, such as: 519-555-5555\n";
            }
            if (!rePostal.test(validPostal.value.toUpperCase()))
            {
                errMessage += "Please type in a valid postal code, such as: N2N3M8\n";
            }
            /*if (!reEmail.test(vaildEmail.value))
            {
                errMessage += "Please enter a vaild email such as: example@example.com\n";
            }*/
            //if no number is typed then show error
            if (isNaN(myForm.pizzaNumber.value))
            {
                errMessage += "Please enter a valid number of pizzas\n";
            }
            else if (myForm.pizzaNumber.value == 0)
            {
                errMessage += "You must order at least one pizza\n";    
            }
            else if (myForm.pizzaNumber.value > 10)
            {
                alert("Please contact this number to place orders larger than 10")
            }
            
            //Check to see the if the Pizza Size has been selected
             if (!(document.pizzaForm.pizzaSize[0].checked) && 
                                                !(document.pizzaForm.pizzaSize[1].checked) && 
                                                !(document.pizzaForm.pizzaSize[2].checked) && 
                                                !(document.pizzaForm.pizzaSize[3].checked))
             {
                 errMessage += "You must select a pizza size\n";
             }
             
             
             //calculate order
             if (!errMessage && (document.pizzaForm.pizzaSize[0].checked))
             {
                 finalAmount = pizzaAmount * 5;
                     if (document.pizzaForm.extra[0].checked)
                    {
                        finalAmount = ((pizzaAmount * 5) + 2);
                    }
             }
             else if (!errMessage && (document.pizzaForm.pizzaSize[1].checked))
             {
                 finalAmount = pizzaAmount * 10;
                     if (document.pizzaForm.extra[0].checked)
                    {
                        finalAmount = ((pizzaAmount * 10) + 2);
                    }
             }
             else if (!errMessage && (document.pizzaForm.pizzaSize[2].checked))
             {
                 finalAmount = pizzaAmount * 15;
                     if (document.pizzaForm.extra[0].checked)
                    {
                        finalAmount = ((pizzaAmount * 15) + 2);
                    }
             }
             else if (!errMessage && (document.pizzaForm.pizzaSize[3].checked))
             {
                 finalAmount = pizzaAmount * 20;
                     if (document.pizzaForm.extra[0].checked)
                    {
                        finalAmount = ((pizzaAmount * 20) + 2);
                    }
             }
             
             
             
        var boxCheck = 0;
        //loop the topping amount to see if it has been checked
        for (var i=1;i<=11;i++)
        {
            //boxname has a value of topping plus a number incremented by 1
            boxName = "topping" + i;
            //toppingAmount now holds a value of the amount of box's checked times 0.75
            toppingAmount = boxCheck * 0.75;
            if (document.pizzaForm[boxName].checked)
            {
                //if a box has been checked then increment
                boxCheck++;
            }
            
        }
        
        if (boxCheck == 0)
        {
            errMessage += "you must select at least one topping\n";
        }
        else if (boxCheck > 5)
        {
            errMessage += "You can only select a maximum of 5 toppings\n";
        }
        
        //if there is no error box show the total order amount
        //THIS WILL ONLY SHOW AN EMPTY ALERT BOX
        //NOT SURE WHY
        if (errMessage == "")
        {
            alert(summ);
            //return true;
        }
        //if there are errors show error alert box
            alert(errMessage);
            //return false;                                    
    }
    
</script>

<title>Order Exercise</title>
</head>

<body>
<!--Personal Information Groupbox -->
<h1>Pizzaria</h1>
<form action="WF/assign2/pizzaForm" method="get" name="pizzaForm" id="pizzaForm" onSubmit="checkName()">
<table width="475" border="0">
    <tr>
      <td width="329">
<fieldset style="width:250px">
<legend align="top">Personal Information</legend>
First Name <input name="firstName" type="text" id="firstName"  /><br />
Last Name <input name="lastName" type="text" id="lastName"  /><br/>
Address <input name="address" type="text" id="address"  /><br />
City <input name="city" type="text" id="city"  /><br />
Province <select name="province" onClick="checkProvince()">
  <option value="" >Please Select a Province</option>
  <option>Alberta</option>
  <option>British Columbia</option>
  <option>Manitoba</option>
  <option>New Brunswick</option>
  <option>Newfoundland and Labrador</option>
  <option>Northwest Territories</option>
  <option>Nova Scotia</option>
  <option > Nunavut</option>
  <option>Ontario</option>
  <option>Prince Edward Island</option>
  <option>Québec</option>
  <option>Saskatchewan</option>
  <option >Yukon</option>
</select><br/>
Postal Code <input name="postalCode" size="9" maxlength="6" type="text" id="postalCode"  /><br/>
Telephone <input name="telephone" type="text" id="telephone"  /><br />
Email <input name="email" type="email" id="email" />
</fieldset>

<!--Order Information Groupbox -->
</td>
      <td width="130">
<fieldset style="width:300px">
<legend align="top">Order Information</legend>
Number Of Pizza's <input name="pizzaNumber" maxlength="2" type="text" id="pizzaNumber"  /><br /><br  />
Size<br />
<label>
      <input name="pizzaSize" type="radio" value="radio"  />
      Small</label>
    <br />
    <label>
      <input type="radio" name="pizzaSize" value="radio"  />
      Medium</label>
    <br />
    <label>
      <input type="radio" name="pizzaSize" value="radio"  />
      Large</label>
    <br />
    <label>
      <input type="radio" name="pizzaSize" value="radio" />
      Extra Large</label><br  /><br /><br />
Crust Type <select name="crustType">
<option>Hand-Tossed Pizza</option>
<option>Pan Pizza</option>
<option>Stuffed Crust</option>
<option>Thin Crust</option>
</select><br /><br />
Toppings<br />
<input name="topping1" type="checkbox" id="sausage" />Sausage
<input name="topping2" type="checkbox" id="pepperoni" />Pepperoni
<input name="topping3" type="checkbox" id="beef" />Beef
<input name="topping4" type="checkbox" id="bacon" />Bacon<br />
<input name="topping5" type="checkbox" id="chicken" />Chicken
<input name="topping6" type="checkbox" id="ham" />Ham
<input name="topping7" type="checkbox" id="olives" />Olives
<input name="topping8" type="checkbox" id="pepper" />Peppers<br />
<input name="topping9" type="checkbox" id="tomatoes" />Tomatoes
<input name="topping10" type="checkbox" id="mushrooms" />Mushrooms
<input name="topping11" type="checkbox" id="pinapple" />Pinapple<br /><br />
Extra<br />
<input name="extra" type="checkbox" id="extra" />Add small (5 wings) for an additional $2.00
</fieldset>
<input name="Submit" type="button" id="submit" value="Submit"  onClick="checkName()" />
<input name="Reset" type="reset" id="reset" value="Reset" />
</td>
    </tr>
  </table>
</form>
</body>
</html>