I had my last period between 22 and 26 February. My ovulation day was the 7th of March. so my boyfriend and I had sex on that day and two days after. On the 13th i took a urine preg test. It came out negative. Now today 17th, i have what feels like period pains, and i am bleeding. im only scheduled to start with my periods on the 21st of March. What could this be.