Pink/red mid-cycle bleeding

I'm at CD 15/4 DPO and I experienced some bleeding today. I had sex once per day for the past 7 days straight to make sure I had sex a few times before my predicted ovulation and a few times after. Today I had some pinkish reddish bleeding. My period is predicted to start 12 days from now. Any thoughts on what this could be? Thanks for your advice.