What Is The Raised Skin Colored Spot That Burns?

I have a spot on my upper left side of my back (back side of my shoulder) it is a raised spot. A couple years ago it was round the size of a pea and one day puss came out. It is bigger now and stings when I'm at work (at a computer sitting). Sometimes it feels hot (internally not to the touch) and it stings or hurts bad. Sometimes hurts to the touch. It is skin colored and the size of a dime. Sticking up about no more than a quarter of an inch up. Any ideas?