Horrible cramps after sex...

So last night my boyfriend came home after a week of being away at work, and of course, we got it on. He is imo bigger then most guys and when we first started having sex, it would hurt when he put it in all the way. Eventually I got used to it and it started to feel good. But last night when he was putting it in all the way, it still felt good but after he finished my lower abdomen was KILLING me. I was literally laying in fetal position in the bed because my whole body felt crunched. It hurt to straighten my body, it was like period cramps but much more intense. Dies anyone know why this happened or what caused it?