What Causes Brownish Discharge During Menstruation?

Hi - my boyfriend and i had sex regular around the time of ovulaiton - i started having cramps on my ovaries, my uterus, some creamy white discharge for about 2 weeks b4 AF. HPT was negetive though. My breasts have a burning sensation and then i was a day late for period which was shorter and lighter than normal, then a day later i started having a brown discharge for a day, light red spotting. I don't know whats going on because two weeks prior AF i really suspected pregnancy. Please help