Hi, I Am Having A Bad Rash On The Below

Hi, i am having a bad rash on the below right forearm for 3 days before going to the GP. Total for about a week before finally meeting a specialist and being prescribe with the acyclovir pill. The specialist doctor's provisional diagnosis is herpes-zoster. Now its been 2 weeks and seems like few more spots appearing at other place of the body.
What is really happening? The rash do not have any bubbles and they are not painful, but itchy.