My period hasn't been on since June 17th and that day I had unprotected sex on my period and it went off instantly. I have been having very bad back pain & my period has been acting like it's going to come on but never does. I also took a pregnancy test at the end of June because I was really scared and it came out negative! Now it's August 15th and I still don't have a period and my back is hurting really bad!!! What do y'all think is going on???