During Sex

So we were having sex and my Nan’s does not have a big dick sadly but he knows how to use it. Anyways I usually start off on top and every once in a while I get a pain towards my left sometimes I can keep going sometimes I just need to change positions sometimes I need to stop. Today I needed to readjust so I was on my back and I like it rough so he started up and it started hurting and all of a sudden I got a sharp pain in my lower stomach/left hip area and literally hurt for like 5 minutes straight I was in tears. Where is it happening and why? I’m not very good with figuring out anatomy and stuff.