What Causes A Pimply Red Rash Only On The Upper Chest?

I have a pimply red rash only on my upper chest. It was here a week ago and then vanished. Yesterday it came back. Benadryl, hydrocortisone cream, betamethasone cream and gentamycin cream has not made it any better. It is not anywhere else on my body. Could this be from stress or would it be a viral something? Curiosity is eating at me to where I dont know if I should go to the dr for this or if I am worrying oer something that is nothing... Thanks