If you say this has been going on for 3 years, then it's almost crtainly not cancer. Nipple pain is almost never a sign of breast cancer, and if it was, it certainly would have progressed to an obvious problem in those 3 years. My best guess would be a hormonal issue of some kind; perhaps exacerbated by a skin issue. Maybe one nipple is simply much more tender than the other, and is responding to a harsh bath soap, something in your laundry detergent, or a bra that doesn't quite fit right. Next time you visit the doctor, ask about this, and if there's anything you can do to help with the pain. Or, if it suddenly gets worse - if it seems infected, for instance - then best to see a doctor right away, OK? Good luck - PJH