2-week rash with no other symptoms??

[edwardcullensotherwoman]

DS has had a rash on his upper body for the past 2 weeks. It started as reddish pink spots, then became pink blotches. It's not raised,in fact I can't feel it at all.

No temp, a bit of a sore throat and cough since Friday but that's it.

He's had every blood test going including allergies. FBC normal.

Any ideas?

Has he been checked for slapped face? When dd1 had it, the most obvious was her body looked like she had sun burn in blotches over her limbs. It only became clear that it was slapped face when dd2 came out with it, and it was much more conventional symptoms.

He's seen a GP, nurse practitioner and a haemotology consultant (to do with ongoing health issue, not for the rash) but none of them have suggested it. I wonder if that would come up in any of the blood tests?
It doesn't have the "fluorescent" look of sunburn though, IYSWIM? In fact it looks a bit like a scarlet fever rash, but not raised. Everyone who's seen it has said it looks viral, but odd how there are no other symptoms of a virus. Consultant not convinced, but he couldn't say what he thinks it is