There is a genetic test for HNPP, have they done that? Your father's elbow problems sound a lot like mine, but I simply have pinched nerves in addition to hereditary neuropathy. HNPP comes and goes, my symptoms are pretty much permanent. There may be more than one thing going on with the diversity of symptoms you have described. It must be very frustrating to have to wait for more aggressive diagnostics, and you are right, time may be essential to recovery.
I hope that you get more satisfactory answers soon. The questions that the others have asked are an important place to start. Finding a cause for PN requires that you be a detective, and even the most seemingly insignificant event or medication can be important. Toxins, antibiotics, cholesterol medication, tick bites, alcohol, ruptured discs, vitamin deficiencies, and many other things can all be causes, so keep meticulous notes. Doctors tend not to want to assign blame to any medical treatment, but unfortunately many of them do carry a certain risk, which is why so much of the research has to fall on the patient and his family.