--that may well be related to your symptoms, given your low B12, and the anemia that responds to iron (at least when you're on it), have you ever been tested, either serologically or by endoscopic biopsy, for celiac disease?

There is the possibility that you have both spinal issues and autoimmune ones--none of us are spared the possibility of co-morbidity, unfortunately. And when people have more than one condition the investigation/diagnostic process is just that much more confusing.