Ouch !
You're fit to fly......when you're fit to fly.
Best case scenario, when the lesions settle, aprox 7-21 days, (AME can advise you best.)
Post herpetic problems (usually pain) can affect patients for many months, the agents (drugs) used to control the symptoms are probably more of a problem, in terms of flying, than the pain. Sometimes the odd twinge can be controlled with regular paracetamol, which doesn't seem to cause many problems for pilots.