new to birth control pill

I started taking the pill the end of december, during the first 2 weeks on the pill i took the pill everyday. I didn't take at the same time, but usually withing an hour ot two from the the day before. I had unprotected sex twice im January, the first time was in the middle of the month and the second was towards the end of the month. Right after sex the second time, when I got up, I immediately had a lot of reddish discharge that went down my leg. Recently, I have started to have waves of nausea, it's really bad in the morning. I am more tired than normal and have this lower back pain that comes and goes through out the day. I have also noticed that I am more emotional. A friend suggested I take a home pregnancy test. The box, came with 2 and both came back negative. I stopped taking the pill a week ago. Since the tests came back negative, I am assuming I am not pregnant. Could it be side effects to the pill or stress ot what???