Brown Discharge and Cramping?

Okay so me and my boyfriend had sex about three weeks ago and he started without a condom for a couple of minutes and then he put one on to finish. Yes I'm aware pc contains sperm and this is why I'm nervous. About a week after we had sex I started having a burning during urination so I went to the nurse at work and she did a pee test on me that came back negative and she said she thought I was beginning to get a uti. She prescribed me medicine to prevent me from developing one. I took the medicine as prescribed and the symptoms went away. About a week later I started having a brown vaginal discharge so much so that I wore a tampon. This went on about a week. That thursday I was due to start my period and on that day I did have a little bit of bright red blood on the tampon and then the next day I had a little discharge and it stopped. My periods wernt normal in high school and i was put on birth control to regulate them but i eventually stopped taking them because it was making my period cramping unbearable. When i started having sex regulary with my bf now they seemed to regulate themselves. Worried, I waited until four days after I was supposed to start and I took a pregnancy test (the early detection ones) and it came back negative. So later on that evening I took another one and the next morning (Tuesday morning) I took another one and they both came back negative. I am having no pregnancy symptoms; no fatigue, no snelling enhancements, no tender breasts, no morning sickness. A couple days before I was due to start my period I got a little bit of acne (normal for when I'm bout to start my period) and I felt bloated (also normal). Well today I started cramping and having the brownish/red discharge again and it looks like a creamy blood ( nasty I know). I was just wondering if maybe this all this discharge is my period? Or Is is it likely that I'm pregnant? Or is it possible My periods went back to being irregular? Please someone help I'm so confused