I would be very concerned and get to a doctor immediately.
your breast is probably sweating or something...
try putting a light coat of deodorant where the odor comes from... :)
it should help...
In my opinion you should have your breasts checked by a medical professional to make sure there is nothing serious.Odors sometimes is caused also by a Fungal/yeast infection and a dermatologist would be better suited to detect this problem.Please go to have this problem checked.Take care.
I just reread you post,and noticed that you are talking about a discharge from your nipple?,in that case Fungal/yeast infection would not be the cause of the bad odor but a problem with the breast itself.Yes,seek medical advice,the sooner the better.