Me and my long time girlfriend had sex for the first time about 3 weeks ago. Throughout the month we have had sex 4 times, every time we do have sex i use a condom. I did not c*m during intercourse because it only lasted a few minuets because it started to hurt for her, and she told me there was a brownish liquid coming out of her. We bought a pregnancy test and it confirmed she wasnt pregnant, but she is a few days late on her period, what could be going on?