Sex hurts in some positions

Sometimes I get this awful pain when I’m having sex with my bf and sometimes it’s followed immediately by bad cramps, so bad that I usually start crying sometimes.

They usually happen when I’m doing doggy style but only when I’m more bent over and my back is kinda arched. It depends on the angle. And sometimes when I’m on my back and he’s pounding into me, it’ll be fine but then all of a sudden one trust will hurt. So whenever we do those positions he knows to start slow and not too hard so I can feel it out. And when we’re doing doggy style he always lets me take control at the beginning to feel it out bc sometimes it doesn’t hurt and I can usually tell right away if it will or not. Sometimes it way worse that other times.

Has this happened to anyone? It really worries me. We’ve been having sex for 4 years now and I think it only started a year or two, but that’s probably just bc we starting having more intense sex compared to the beginning. (We are both each other’s first and are both 22 rn)