I'm on the pill and im 18 the day my period ended completely my boyfriend an I had unprotected sex I took my pill that day and the day after the next day I was at work and had forgotten it that morning my stomach was cramping slightly an a lot of lower back pressure I went to the bathroom to find out there was blood not a lot but enough to be seen it was a bright pink not a dark red as soon as I got home I took my pill. My bleeding only lasted that day what could it be?