How Can Whole Body Rash Be Topically Treated?

we are on vacation in different region of country, my 2 year old son broke out in a full body whelty rash...no real fever, no other symptoms. he has had it for 3 days now. took him to dr. yesterday and she didn't know what was causing it...prescribed internal antibotics and a steroid, but nothing topical. last night he scratched himself raw and broke out again...what can i do topically and is he recieving appropriate treatment?