Bad stomach aches after sex

This is my first time posting anything on this app so be kind please😂

Me and my boyfriend have been together for a year and a half, we have been very sexually active the whole relationship but recently Iv started to get bad stomach aches after sex, the stomach aches last for a long time and hurt so much I cry. It doesn’t happen every time but it happens often.

Does anyone know what it could be?

Thank you😊