What Causes Pus Filled Lump On Upper Chest?

On my upper chest I had a pimple. After the pimple was gone I noticed that there was a average sized lump where the pimple had been. It isn t a wort because it looks as though it has pus inside but it kind of has a skin shell type thing on it. I would like to know what it is, and how to get read of it. Thank you