For the time being, apply an over-the-counter antifungal to the area like Lotrimin or Tinactin. If the fungus is spreading quickly, though, it might be a systemic problem in your body, that is, the fungal population in your body as a whole is so large that your immune system can't keep up with it. If that is the case, you will want to start thinking about improving your diet (omitting foods with refined sugar, foods made with grains such as breads and pasta, foods containing fungus or yeast such as mushrooms), taking an antifungal internally, and supplementing with a good probiotic to replenish the good bacteria and flora in your body as the antifungal thins out the fungal population.
Here is an article on how to get fungus and yeast under control:
You can also learn more about how to get fungal and yeast problems under control at the Candida Support Forum here. (Fungal and yeast overgrowth problems are similiar and have the same treatments.)