My son has woke up this morning with a few raised red lumps they have now progressed into large red blotches on the tops of his arms,legs and a few on?

Possible hives: Without a photo or exam, large blotchy rash sounds like hives, but 5th disease, a common viral illness, starts with flushed cheeks and then progresses to a blotchy, lacy rash on the outer parts of the arms and legs and sometimes the chest. Hives are usually itchy, may come from an allergy to a med or food or body reaction to recent illness. Treat with oral Benadryl, (diphenhydramine) etc. Fifth disease not itchy.