What Causes Discharge Through The Nipples And Hard Skin At Center Of Nipple?

Hi, I am 23 year-old healthy female. Three years ago I noticed that I was geting slight discharge from the centre of my nipple, I was not overly concerned as it was very little. I am on the contrceptive pill now for three years. A few months ago, I have noticed that there is a much larger accumulation of yellow and green hard skin in the centre of both my nipples, but particularly the right one. I do not know if this is a common symptom of the min-pill or a dermatological condition. Any advice would be appreciated.