I am sorry about your significant medical issue. I am writing to you with an answer on the basis of your initial information. I would be happy to discuss it further if you provide me more information.
You should be looked for;
1) A spinal issue
The following investigations would help you ascertain the cause;
1) Electromyography/nerve conduction studies (EMG/NCS)
2) MRI of the spine and brain
3) blood glucose, glucose tolerance test, and glycosylated hemoglobin
4) serum B12 level with methylmalonic acid (with or without homocysteine),
5) serum protein electrophoresis
6) Antinuclear antibody
7) Lyme testing
8) Rheumatoid factor
9) Sjogren's syndrome testing (Anti-Ro, Anti-La Antibodies)
Wishing you a speedy resolution and all the very best in life.
It was a pleasure to assist you.