How can I stop itchy spotty rash keeping me up at night?

GETTING TO THE HEART OF MEDICAL MATTERS

- Dr Rosemary Leonard

I've suddenly developed a red, spotty, really itchy rash on my chest, back and upper arms.

Being a typical slightly older bloke (I'm 60), I tried to ignore it to begin with, but it's been going on now for at least a month and even I realise I can't carry on scratching. It's disturbing my sleep, though otherwise I'm quite well. The chemist suggested I try an antihistamine cream but it hasn't made any difference. I tried ringing the surgery for an appointment but got stuck in a long queue so gave up. Is there anything else I could try that I could get from the chemist?