Itunes uses the first email address you register with as your ID. This becomes part of your purchases of iTunes media. If you change your email address, you should alter your profile to show your new email address but your ID will remain as your original email address (it doesn't use it for email just as an ID). You now have two iTunes accounts holding separate purchases so you can update one, then you have to log into the other to update those purchases. Your password for the original account doesn't work, normally you can ask for the password to be sent but it will go to the original email address. So no good to you. Send an email to iTunes support explaining the situation and asking them to reset your account(s)
Go here
http://www.apple.com/uk/support/itunes/
then click Itunes store account & billing, then manage your account, then click the email icon