They started off looking like hives (raised white lumps surrounded by redness) but are now red spots. Not blister-like. They're itchy and sore. He has no temperature or other symptoms.
He's never had chickenpox.
Pretty certain they're not bed bug bites as have inspected bed/mattress thoroughly and also the mattress is only a few months old.
He does have sensitive skin in general but has never had these before.
Any ideas?