Swollen abdomen for days after ?

I have been sleeping with my boyfriend for a month now and a week ago I had to stop in the middle of because I was in so much unusual pain. my lower abdomen has been swollen and hard as a rock since then and has not let up (not even with a pain reliever) I have not been able to have since then because it's just constant pressure and pain. what could this be? I have had a child - this was 2 1/2 years ago tho.