Sore nipples?

I suspect I O'd on CD 21 (The CM matched up and I had a little ovarian/uterine pain, which doesn't happen during my anovulatory cycles) and for a while my nipples were sore, but I hear that's common after ovulation. I'm on CD 28 and my nips are on the tender side of normal (Not quite sore bit still a tiny bit sensitive.) I haven't treated them any harsher. Any idea what's going on?