Note, if you create an new Apple ID, it will have no content associated with it, any purchases, made with your original Apple ID will remain tied to it. In the case of Apps they will continue to request that Apple ID and cannot be merged oer transferd to the new Apple ID.
Unless the Apple ID belonged to a company and not you, what you want to do is edit your existing Apple ID to use a different email. That way all purchases and content remains with it, and you can continue to access it normally.
As mentioned by Eric, the email must not have been associated with an Apple ID in any way for it to be able to be used as a primary email address for the Apple ID.
You may need to acquire a new email address from a provider such as Hotmail, Gmail, Yahoo, etc..