It does sound like you've been through the wringer.
One of the interesting things you mentioned is that during cancer therapy, your pain decreased, rather than increased; the latter has been the expereince of most people during chemotherapy, as most of those drugs, especially the ones that are metal-base, are highly neurotoxic. I wonder if you may be having a delayed reaction (chemotherapeutic neuropathy does take a while to develop). Is your pain now exactly in the same spots your shingles pain was? That would be unusual, though since the nerves in the distribution are already damaged, it wouldn't take much to set them off again (through what is known as the "double crush phenomenon") . . .
Come on over to the Peripheral Neuropathy part of Neurotalk:
http://neurotalk.psychcentral.com/forum20.html
Lots of us talking peripheral nerve damage (from various causes--and causes unknown) there.