Unusual pain after sex

My boyfriend and I have been sexually active for months and I was on birth control until I forgot this last month. I got my refill but we have still been having unprotected sex and he's been pulling out. Recently after sex my lower stomach starts painfully cramping to the point of tears. I don't know if there is any correlation but I just want to know if anyone has anything to say about it. It's happened the last 4 times maybe. I plan to make a visit to the doctor if anything.