Random abdominal pain during sex?

So, during me and my bf’s second time having sex today, I suddenly got this weird lower abdominal pain, close to the pelvic area, almost like a period cramp but more subtle? It’s only happened a couple more times this year, all at very random times. I just really wanna know any potential causes to this. (Just a heads up, I had eaten a sandwich and was quite full. But I don’t remember if I had eaten as much before the other few times, so I don’t know if I should pin the blame on the food lol). help!!!