Suggest Remedy For Itchy Rash On My Limbs And Chest

I have a rash on my arms chest and back of my legs. The Doctor has prescribed antibiotics for a month and cream which I have taken and done absolutely nothing. Also I was prescribed an antihistamine which did not help either.
It seems to be worse in the evenings and when I go to bed. Can you please suggest something which might relieve the itch.