I need help!! My boyfriend and I had sex for the first time on November 19 and I was on birth control for over two weeks and and also used a condom. My birth control that I'm taking stops my period. I recently stopped taking birth control to change the medicine. I also had my period on November 25 to 29 and I haven't had my period since. My period was supposed to come 13 days ago and nothing has happened. I need help!! I also took four pregnancy test before my predicted period and all negatives. But I've been having stomach pains and back problems. Please help me