Because of the PN you have probably changed a good deal of your 'lifestyle', haven't you? You are less inclined to 'go out', if at all. It's fact that atheletes [for example] 'come back' IF they start exercising soon after injuries. Why? muscle tone is lost, tendons SHRINK/tighten and, well things go downhill from there. Dramatic changes are of those long-term bedridden folks...it's a slow gradual and deteriorating process.
I would go w/the PT route, BUT only after checking out what area PT services are. You may get a therapist who's no CLUE about PN and you could be one unhappy camper after one session...Going and watching, seeing how therapists treat their different patients, well, you can get a good feel of a place, and if it's for you. I've had 5 'rounds' of PT in my 4 years of PN/CIDP., tho two were for foot/knee rehab after falls. I'm still walking [tho not far] and driving and will continue to try and keep doing so!

As for seeing a rheumy or even another PN doc, those second opinions may or may not get you a clearer diagnosis, but if the extra 'input' costs you just the co-pay, what have you got to lose? To me, it's a no-brainer, in that it puts a new brain, and pair of eyes and ears on your case....& maybe get you more tests, or an impetus to your current doc [that old peer pressure thing] to do the needed tests and get you on your way.

Have you tried the glucosamine/MSM supplement route? Just another thought to put into the already confusing mix.

Hope this helps! - j