Hello. I Have A 28 Day Cycle. Last Period Was

Hello. I have a 28 day cycle. Last period was on oct. 16th. Lasts 4 days. I had unprotected sex on nov 2nd. My next period is due nov 13th. I started bleeding last night. Very light. Since thwn ive only used 2 tampons. I have lower abdominal cramps. Headaches. And ive been more tired than usual. According to my period tracker i had sex 2 days after my scheduled ovulation day. What could this be?