I lost my balance when I updated my apple ID email- has this happened to anyone, and if so, how can I get my balance back?!

Updating the primary email address on an account should not affect its balance nor its past purchases. You've checked your account's purchase history (See your purchase history in the iTunes Store on a Mac or PC - Apple Support) to see if anything could have used the balance e.g. auto-renewing subscriptions, pre-orders ? If you can't see where it went, and you've tried logging out and back into the account, then contact iTunes Support for your country : http://www.apple.com/support/itunes/ww