R.N.
Hi S.,
If I were you I'd have my OB/Gyn check it. It is probably something benign just like the othe two posters have said, but I know I wouldn't be able to rest easy until my doctor checked and confirmed that it was 'nothing.' I have heard of women discovering they have breast cancer while nursing, and I'd hate for you to overlook something possibly dangerous b/c you think it is just a by-product of nursing.
I don't at all want to scare you, I just think it is better to be safe than sorry! Good luck. :-)