Could I still be pregnant?

I'm currently in the middle of a menstrual cycle. Two menstrual cycles ago I had a light period with very light bleeding when it happened. However, I took a pregnancy test about two weeks later that was negative. I had been worried because, while we used a condom, I had been flaking on the pill. A couple weeks later I had again (I don't remember ovulating, but I may be wrong), after being on the pill at the same time every day and using a condom. However, a week and a half or so later I missed my period again. I have taken four pregnancy tests since then, all negative -- but I know there can be false negatives. I've had few symptoms (none of the common ones), but I did have bad unexplained leg pain for a couple days and some back pain, but I also know that not every woman has symptoms. I was supposed to get my period this week, and I thought I had due to heavy cramping, but it's just small amounts of brown discharge at the moment, which happens at the beginning of pregnancies. I've also heard that even if you do have some bleeding, you may still be pregnant. I'm planning on taking another pregnancy test in a few days, but am I just being paranoid? Is there actually a chance that I might be pregnant? Or is it likely just how the pill has started to affect me? Thanks.