Hi everyone,
I am new here, I have been reading here for a while and got much more information from this forum than from my doctors, thanks!
I am seeking desperately for a diagnosis and treatment and would appreciate any help.
I apologize for the length of my message and for English mistakes, I am not a native speaker.

I am coping with debilitating health problems for many years, it seems it might be caused by an autoimmune disorder but I don’t have any definite diagnosis.
It all started almost 20 years ago with extreme fatigue, Postural orthostatic tachycardia syndrome (POTS), dry eyes, joint pain, Adie tonic pupil and trigeminal neuralgia. A few years later I got Lymphoma and underwent a chemotherapy (which included among others Rituximab, and Prednisone). After the chemotherapy I felt much better than I felt in years, but after 1-2 years my energy gradually deteriorated up to the point that I can hardly get out of home and spend most of the time lying in bed.

I am vegan , I keep a healthy diet based on vegetables, fruits, legumes, nuts, whole-grain etc., almost no processed food and preservatives.

A few months ago I was diagnosed with SFN, skin biopsy showed severe reduction of small nerve fiber innervation, and moderate reduction of autonomic innervation. I have got numbness, tingling, burning etc., but my symptoms are mostly reduced sensation and not severe pain. Is it normal ? Is it going to progress and cause pain ? Can these symptoms give any indication for the cause of my neuropathy ?

It is assumed that I probably have an autoimmune disorder, but I don’t have any specific diagnosis.
My insurance denied IVIG because without any specific autoimmune diagnosis I don’t meet their criteria.
I had allergic reactions to Plaquenil and Imuran.
Are there any other relevant treatments ?

Tests
All tests for Sjogren, Lupus, Celiac, MS, Myasthenia were negative. Except for ANCA, ANA, Anti histone that once were positive/borderline, and later negative.
Anti gliadin was positive (the rest of the celiac panel was negtive).
No diabetes - Fasting glucose ~85mg/dl (lab range 70-100), A1C 4.5% (lab range 4-5.7).
All the routine tests are negative.

Supplements:
- When first tested I had extreme B12 deficiency 99pmol/L (lab range 180-700). I take 100mcg (cobalamin) daily and the blood levels are about 300-450pmol/L. I have read on this forum that the supplements should be stopped before the tests, I have never done it.
- My D25 level was 21.8nmol/L (lab range 5-250), I am taking 2000IU D3 daily and the level now is about 70-80.
-Other supplements: CoQ10 100mg, vit E mixed tocopherols 400IU, vit C 500mg, Calcium 600mg.

Sometimes I use Provigil for the fatigue, can’t take it often.

I read about the ACh receptor autonomic ganglionic ab test and would like to do it. I understand it is usually done as a part of the paraneoplastic antibodies panel, but since I already had my share of cancer, is it worthy to do the other tests ?

I would appreciate any suggestions regarding diagnosis, tests and treatments.
Thanks!