About a week ago, I noticed a rash on my arm pit. It sprang out of nowhere. It's red/pink with small puss-filled bumps. It burns a little, more when I moved my arm or stretch the skin around it. It doesn't appear to be spreading quickly, if at all. I have been putting hydrocortozone cream on it for a couple of days, but it doesn't appear to be getting better. I don't have a fever or a cold or other symptoms. What is it? I don't have health insurance at the moment.