What Causes A Swollen, Pus Filled And Red And Peeling Skin Rash?

My friend has had this rash on her leg for over a month now. The doctor she goes to just keeps perscribing her different creams for either staph, fungal infections or herpes. This rash has become very swollen, pussy and red. Recently it has shrunk in size, become very dry, more pale in color and is beginning to peel. It seems as though the antibiotics she was given, bactrim being one of them are working. But there are these strange black dots appearing on the rash now. What could these mean?