Mysterious itchy rash

[BettyBoo246]

My 6yo ds has developed an all over extremely itchy rash. It started around 3-4 weeks ago. The doctors are baffled and have ruled out bed bugs, scabies, heat rash, eczema etc. Tried antihistamines and hydrocortisone creams but nothing seems to really help.
It's worse after a bath and at night time. He's got scratches all over himself and it's starting to affect his school work (teacher has mentioned him itching constantly and being distracted by it)
When it initially started I had changed the laundry conditioner from lenor to comfort, 2-3 days later he started itching so I immediately changed to fairy and re-washed everything but he's still getting worse if anything (gp has said if it was this the itching would have settled down by now)
Sorry for the essay I'm just at a loss now as to what to do next, got another docs app tomorrow but dont hold out much hope

Poor little lad. Have you tried Piriton liquid? My little lad (also age 6)had hives all over him a few months ago after being poorly for a few days with fever and runny nose and cough. Took him to the GP and was told it was a reaction to him having a virus. Cool baths and Piriton we found helped. Also try Eurax cream to help with itching. It's very good!
Has he eaten anything different?

Also, could it be something you are using in the bath water? Hope it calms down for him soon

DD2 has very reactive skin and has been itchy like this in the past, we have it mostly under control now. I would suggest swapping to a sensitive laundry liquid like Surcare and cutting out conditioner. Extra rinse if your washing machine has that option. Also no bubble bath, don’t use soap on his skin. Avoid being too hot at night, sweat seems to make it worse and so does dry air from heating. Maybe a bowl of water in his bedroom to add moisture.

Unlikely to be viral I think if it was set off by conditioner and has lasted weeks?

Have a look at pityriasis versicolor - it's a fungal infection. My DH gets it occasionally, and it's treated with an antifungal skin wash.

Thanks I'll mention some of these to the doctor today. They advised no soap or bubble bath to see if that helps. He's had viral rashes before that only lasted a few days and not itchy.
The doctor said the last time we went if it doesn't settle down they will treat him for scabies? But surely we would all be affected if it was that.
I'm going to get some different laundry detergent and try that too.
The antihistamine we are using is just the chemist own brand so might try piriton instead.