Stabbing nipple pain??

I'm two days away from my due date and for some reason the last two hours I've had this stabbing pain in just my left nipple. It's not a constant pain but will hurt every few seconds on and off. I've been producing colostrum for about a month now and tender boobs haven't really been an issue. It's only in one side right on the tip and it won't quit hurting. What could be causing it?? I was checked today and dilated to a 3 and I've been having occasional contractions and some cramping if that matters at all.