What Causes A Itchy Rash On The Thigh?

I developed a small bruise on my right thigh which has now become a medium sized itchy and at times weepy one. Saw my GP who wanted a swab. But I am unable to swab it as I managed to keep it dry with antihistamine and paracetamol as I have been getting hot and cold sweats in the night and itchiness . However I notice the rash to continue to my right bottom. So help with ideas please. Thank you