I think you need several doctors to sort out this complex situation--probably at a high level facility/university setting.
I would test you for a variety of thyroid and auto-immune disorders, having seen similar situations with vitamin D
deficiency and certain B vitamin deficiencies, though I have to say that yours is the worst case I've heard of.
The doctors recommended would be a neurologist, an endocrinologist, a rheumatologist, and a nutritional expert, all under the direction of a good and curious general internist.
Has anyone ever tried medications like Lyrica that work for nerve pain (like diabetic nerve pain) or Cymbalta?
You have pretty classic symptoms CRPS but generalized.
Is it worth investigating again? It's not a good option NOT to be tested as you only have one life and if you get good years now as a result it's worth it. They may not come to an answer but if you don't take a shot, you cannot hit the target.
I don't think it's psychological but obviously, being in pain like that and having such diffuse symptoms would give you some psychological issues!
Often I recommend biofeedback and neurofeedback and I think that would be a good idea after or even while you are being screened. Why? Because after all these years you probably have the need to integrate the way your brain perceives and learns to ignore some of these symptoms, whether or not they find an answer.
You sound like the ideal patient for a sleuth of a physician.
(further: do you have digestive issues, feel worse after eating certain foods? Has anyone done EMGs/Nerve conduction studies on you--putting little shocks of electricity through your legs, for example?)
What you have may be unusual or unheard of but that doesn't mean unreal. Rare diseases are rare, and some are cases of one.
Phew! That's a lot for you to read and digest!