The Last Time My Boyfriend And I Had Unprotected Sex

The last time my boyfriend and I had unprotected sex was 7/31, my period was due on 8/17 but came a week early on 8/13. I started lightly spotting on 8/12. I seen my OBGYN on 8/18 for my pap but everything seem fine and ruled it as stress related. Plus I took several test before my surprised cycle due to getting symptoms of pregnancy but all neg. Here it is 8/27 a week later and I am bleeding again. What could be wrong?