Cortisone is not as useful as antibiotics, but if it works for you, you could try it. It sounds like the stuff on the back is more of a general infection, though. If you are going to use an over-the-counter product, try for one of the "sporins," like Neosporin or Polysporin. But if they are too mild or don't do much, see your doctor. This is not a difficult problem for a doctor, they see it all the time and know what to prescribe.