discharge coming from only one nipple every month?

I have discharge coming from only one nipple every month during menses for the past four months. I (stupidly) had my nipples pierced 10 years ago, and have had no rings for almost 9 years. Breast tissue surrounding the nipple becomes painful, and upon touching, either while getting dressed or in the shower, a large amount of yellowish, thick fluid is expressed from one of the wholes left by the ring in my left breast. After initial event, a small amount of the same fluid can be expressed manually for a few days. Is this something I need to be concerned about? I am 30 years old and nulliparous.