Many whave small bumps on their areolae (the darkened skin around the nipple). These bumps are the tops of organs called "the glands of Montgomery" or "Montgomery's tubercules"
There are normal organs which help lubricate the areolae by secreting tiny amount of oils onto the skin.
Sometimes these tubercules can become blocked and even infected. Often the blockages can become sebaceous cysts.
Although these cysts are usually not dangerous it would be an excellent idea to ask your doctor - it could be something else, and even it it is not, the matter that comes out of a sebaceous cyst is very unpleasant to smell.
I'm sure it's not an STD; sounds like a furuncle (boil), but hard to tell without seeing it. Go to your doctor or other health care provider.
Good luck-- HHH, MD