Small pink bump on my shoulder?

I have a small pink bump about the size of a pea that is cut in half, on the top of my shoulder. It has been there for about 2 years now, and has showed almost no signs of change. My doctor prescribed me Mupirocin, which is an ointment designed to treat skin infections, and stop the growth of certain bacteria. I used that three times daily, which is what my doctor told me to die, and it has had no effect on it. I need to find out what I have, and how I can treat it.