I'm a bit worried because I had oral sex with my boyfriend and now I'm experiencing a brown discharge from my vagina. It's happening more in the mornings, and I've been having frequent urination throughout the day. This all started after we were together, which was 2 days before my period was supposed to start, but it still hasn't come. I did a pregnancy test today and it came back negative. The date we were intimate was February 26th. What could be causing this?