post sex cramps?

I've recently started taking birth control again so that my boyfriend and I could have unprotected sex ( I know. Not 100% safe, but it feels good and anyone who objects I feel you're lying ). Last night we had unprotected sex and he ejaculated inside of me, and I felt fine. But today, I have really bad cramps. As in, my stomach hurts and I feel nauseous. I ate, but that hasn't seemed to help much. Any ideas as to what is wrong and how to stop it? Please 😩😩