Sounds like you are in terrible pain.

This forum is not a diagnosis forum, and we here cannot "treat" illnesses or
give you expectations beyond that which is on the net.

If you have RSD, that is another different issue. Full body RSD is not
common, and you should talk to the patients on that forum here.

Raising B12 levels is important because spinal cord degeneration leads
to severe impairment and even death.

We cannot separate out your various symptoms on an internet board.
All you can do is take what you know you are low in, and wait/hope that
improvements follow. Rose herself has waited years, but has had steady
improvements with her journey from very low B12 levels that were ignored
by doctors. (until a one day one doctor noticed it).

I am sorry that there is no quick solution for you, in this area.