What Causes Bump On Back?

Hi I had a small to medium sized bump on my back that's been there for about 8 years because my physician said to leave it there or a dermatologist could cut it out. Last night, unlike many other nights, when I went to squeeze it a cream like white substance came out. It had a slight odor to it. Basically, it was like a pimple. The area is not completely flattened yet and more came out today but I scratched away some of the skin with my finger nail and a black freckle surfaced in part of the area. He he. What is this? Am I in trouble here medically speaking? Will it keep coming back? Am I doomed for squeezing it :)