I have an inverted nipple and I want to know who to consult about it?

Thank you for sharing your excellent question.  It is always wise to have a physician assess your breasts for any acute changes that may take place.  That said, if your inverted nipple has been present for 6 years it is unlikely to be the result of cancer, and I would see a plastic surgeon for an in-person examination.  Correction can be performed with a small in-office procedure.  Hope this helps.

. . . if this has indeed been present for years, is not associated with a recent change such as nipple drainage or bleeding (or underlying mass), and you don't have a strong family history of breast cancer.  Very reasonable to start with an assessment by a plastic surgeon (who can fix these things fairly simply, often as a local-anesthesia procedure), but if any of the other above conditions apply (and/or you're due for a mammogram, have that done as well), and have an assessment with a breast (oncology) surgeon, if not at least your OB-GYN who does regular exams and knows your history well . . . better to have early assessment/intervention that to discover a more advanced problem later, but again, probably benign and easily treated (hope so!)

Women should always be aware of the signs of breast cancer.  A nipple that has been normal but then starts to invert doesn't necessarily mean cancer but should be checked into- examination by a breast surgeon, mammogram, etc. You can start with your primary doc or GYN and go from there.  While a younger age makes cancer less likely, it is still possible. 
Since it sounds like it's been stable for 6 years, it's unlikely that you have cancer.  The problem can be fixed with a fairly quick office procedure.  However, at the very least you should have a mammogram and evaluation before planning the procedure.