can i look up my account by my credit card number

No, you cannot. If you've forgotten your Apple ID, go here:

https://iforgot.apple.com/iForgot/iForgot.html

BTW, this forum is for questions from people managing sites on iTunes U, Apple's service for colleges and universities to post educational material in the iTunes Store. Normally you will get the quickest and most applicable responses if you ask your questions in the general iTunes forums.

Regards.