, and welcome to NeuroTalk.
I'm sorry that you're suffering so much and that the pain medications have given no relief. I dare say you already know that post-herpatic pain is nerve pain, and that neither regular pain killers nor opiates work on nerve pain.
As a rule, a combination of one of the anti-epileptic medications and an anti-depressant are ordered for nerve pain. Plus, there are the local anesthetics like Capsaican Creams or Lidocaine patches.
I was lucky enough not to suffer the lingering pain after my own outbreak of shingles, but I sure do feel for you just the same. I can only suggest that you keep the appointment with the pain clinic and try ice compresses and local creams, or patches, until your appointment comes around.
We do have a medication Forum here. You may get more specific advice if you asked there: http://neurotalk.psychcentral.com/forum72.html