It's interesting that your doctor thought it was vitamin B levels. My vitamin B levels were low normal, my neurologist had me taking B12 vitamins, didn't change my situation. My primary care doctor put me on vitamin B12 injections that provided some help with neuropathy.

My wife has been a type 1 diabetic 60 years, there are a few things you might consider doing if not done already: (1) have your kidneys checked. Most of my wife's doctors were concerned with protein "spilling" into her urine, it's sign of kidney disease, (2) check your A1C levels, that will show you just how close you are to being a diabetic and (3) have a sugar tolerance test to determine your body's ability to handle excess sugar.