What Causes Delayed Periods And Stomach Pain?

Hello, I'm about 3 months late with my period now but I'm not sure if this has anything to do with my stomach hurting or not. Yesterday, I was doing a few yoga poses-trying to get fit and everything. Then an hour or two later the lower part of my stomach started hurting. It doesn't hurt if I slouch when I'm sitting but If I sretch my stomach in anyway it hurts badly. What do you think is wrong?