Worried about nipples

For the past week my nipples have hard and really sore :( I thought my period might be coming soon but still nothing. I also noticed that they turned darker around the point of the nipple. I'll probably get it checked out soon but does it seem like something I should worry about? I haven't considered pregnancy as a cause because I haven't felt nauseated or different at all. My periods are hard to track because I usually get one then skip one and my next one is not due til the end of this month.