I had unprotected anal sex with my boyfriend... could i be pregnant?

Yes: If you do not want to get pregnant - or if you have a desire to be protected from sexually transmitted diseases, always use condoms. If you are sure there are no potential diseases, other birth control methods exist. Have a test as soon as the test instructions advise and take care of yourself always. Good luck.

Probably not: Unless some semen seeped from your anus to your vagina.