SO CONFUSED

Ok, so... About a week ago (a little more) I noticed a rash developing on my chest where my seatbelt rubbed. I had driven for several hours and been at the beach for the weekend so I just assumed it was that. The rash was above skin and red and spread very quickly over my chest and has slowly spread to my legs and feet and a little on my arms and hands. The rash on my chest appears in larger patches where as the others are more single. There are never any blisters or real bumps and while it itches slightly, it is not terribly uncomfortable. Prior to the rash appearing I had gone through two doses of antibiotics for tonsillitis and now the dr. gave me some steroids to get rid of the rash because it did not appear to be caused from strep. This is all over my body and is mostly on the backside of my legs, between my heels and ankles, and chest. I havent been sick except for tonsillitis a couple weeks ago and the steroids only have one more day and while my chest looks better, its not gone... What is the world could this be? I have not changed any products that I use...