Cramps after sex

My boyfriend and I had sex like normal. A few hours later we decided to go for round 2. Mind you this was around 2/3am and we were both super tired towards the end. He kept slipping out and eventually hurting me so we decided to stop. We fell asleep and maybe 2 hrs later I woke up with horrible cramps, to the point I wanted to throw up from the pain. Anyone know why? Too much air inside me? He didn’t fuck me hard enough to hurt my cervix so I know it can’t be that. Any tips on minimizing those cramps or how to avoid them at all? Thanks!