What Causes Painful Rashes On Chest?

I have a rash on my chest. It is under my breast and goes down my sternum and spreading to my upper torso. The bumps are filled with white puss and they are also red. The are very painful and hurts to have my clothing touch. I went to the doc and the prescibed cream but it does not allieviate the pain and it is spreading. I feel ill as well...Headache and nausea