I use a period tracker which tells me my fertile days and ovulation days. I had sex using no protection and he came in me everytime on four of my fertile days and one day was before my ovulation day. I always have a regular 28 day cycle. I started my period four days before the app said it was due and the app has always been correct before. this bleeding is also very painful and uncomfortable in my lower back and lower abdomen (worse than usual) i am just wondering if its possible I'm pregnant please help!!!