Are you completely finished with all Hep C treatment, including Interferon and Ribavirin?
I developed a rash at week 10 or so. Benadryl and over the counter Cortizone cream were useless for it. What did work for me was Hydroxyzine 50 mg every 6 hours, Fluocinonide ointment, and Clobetesol soln. They are all prescription.
The Hydroxyzine is an oral antihistamine (stronger than Benadryl) and it was not until I got a high enough dose of Hydroxyzine that the rash and itching finally got under control.
The Flucinonide is a strong steroid ointment which did help. It would clear up the rash after 2-3 weeks but then the rash just moved next door. That is why the Hydroxyzine was needed, to work systemically.
The clobetesol solution (also steroid) was for my scalp but it works on the rest of the body too and it was excellent, worked well.
If you are finished with treatment, hopefully your rash will clear up fairly soon but, in the meantime, you need some stronger meds to use until it clears. It could hang around for awhile. Hopefully it won't.