One sore nipple? What is the cause?

Isabel Asked: One sore nipple? What is the cause?

I woke up 2 days ago with my right nipple hurting. It is mostly just sore to the touch. The areola and surrounding area of the breast is fine, and my left nipple is fine as well. It doesn't seem to be discolored, but it wont stop being sore, and it seems slightly more firm than usual. I've been on ortho tri cyclen for several months, and this is around the middle of my cycle. I know nipple pain is a symptom of pregnancy as well as pms/ovulation but this doesn't seem to fit. I'm not due for my period, but in the past i have had sore nipples/areolas during my period, but this is different. Other sites have indicated hormonal imbalances and yeast infections could be the issue. Any ideas? If so, how can I treat it?