my boyfriend feels sick during sex?

so my boyfriend and i broke up for two months. before this, we had sex almost every day. we've had sex twice since getting back together and every time we do his stomach hurts him so much that he has to stop sometimes. he says he's only ever felt this pain during the two times we had sex, and having an orgasm relieves some of it but not all. what could this be? its kinda putting a strain on our sex life lmao...