Sudden eruption

My son is 7 yrs old and he he has had eczema in the past. We normally are able to get it under control, but all of a sudden, he has eruption all over his body. Some are in clumps but it is all over now. I don't know if it's still eczema because of it's sudden flair-up. Brought him to dr but he said it's not a "text-book" rash. Got referred to dermatologist but there's no appt open until May 4. That's too long for my 7yr old to wait. Benadryl is helping a bit with discomfort but the child looks like a big ball of rash! Please help.
Thanks.