What Causes Bleeding During Ovulation?

I am 37 years old, my weight is 72 and height is 5;20. I had hep b about two years ago but i have been diagnosed as not having any serious problem. Last month i took postinor 2 after i thought i might get pregnant from an unplanned sex. i had my period alright though it came 2 days earlier but after two weeks from my mensturation, during my ovulation i have started bleeding and now i have bled for 3 days