Question about symptoms

So I have a question,.... We've been following the cycle days and ovulation days to be exactly on schedule. We had a 22% chance and a 33% chance the 29 and 30th of November. We're very sexually active and my period isn't for another week. But today, during sex... I started to bleed. It didn't have an Oder or look like period blood. It was a reddish orange color. I had no cramps. So I used a pad at work and when I last checked I stopped bloeeding and I had dark brown blood. My lower abdomen feels like there's a pressure feel to one side. And my breast had been to see and my nipples are super sensitive (like kinda hurt). What could this be?