Help?!?!

So I have been on the pill for about 4 months now so I’m new to all of it and tonight me and my boyfriend were having sex and he was on top and I had to have him stop bc of excruciating pain. I can only describe it as similar to when you have to pee REALLY REALLY bad type of cramping and it’s a little later and I still have that pain just below my belly button I’m really worried and not sure what to do. According to the app my period is 4 days late but tbh my period is never regular and I never start when the app says I am. What should I do?!?!