I am on the pill but had unprotected sex with my boyfriend in between my last periods. My last period was suppose to start on Sept 16. On the 13th I had a little bit of bleeding and I thought it was my period. However I had very little blood and it only lasted a few days. I haven't been feeling real great the last couple of days and have not done a pregnancy test yet. Could I be pregnant or is it more likely just an irregularity in my cycle?