Itchy rash on body and don't know what it is.?

Two days ago I noticed a blotchy red rash on the inside of both of my biceps. The rash also went around onto my back about an inch on my left side. Then the next morning my feet were really itchy but the rash didn't appear there until last night. I had visited the doctor yesterday morning and he said it may be from sweating or something along that line and gave me cream. He told me if it spread it is most likely a viral infection. It did spread down my sides and onto my legs and down my arms and it is very itchy. I have been using the cream it takes away a little bit of the itch but not all of it and I don't know what to do now. The rash isn't as visible as under my arms but you can see it if you look at it closely. What should I do now? Also I am a 19 year old male, and I have had somewhat of a sore throat and a runny nose for about a month and a half but I thought that to be my allergies acting up. I had a strep test and it came back negative.