You need a lot more B12
I understand that B12 deficiency can cause a problem very much like CIDP and that you do not have to have the blood problems. the good news is that the neuropathy of B12 deficiency is more easily treatable. The bad news is that nerve damage is nerve damage and you have not seen reversal of the nerve damage. I work with children with blood problems and B12 deficiency due to lack of intrinsic factor (Pernicious anemia) is very, very rare in children,but when we had a child with this problem and low B12 levels and neuropathy and blood problems for him, he was treated a lot more aggressively than you are getting. I think he had two weeks of daily B12 shots and then 2 months of weekly and then monthly shots. I looked up in a drug book and for adults with pernicious anemia, it is recommended to get 100 micrograms a day into a muscle or under the skin daily for a week and then, if there is improvement, the same dose every other day for the next two weeks. If there is improvement next go to every 3-4 days for 2-3 weeks and finally monthly. At another place, it says for complicated B12 deficiency (with severe anemia, severe neurologic damage, heart failure symptoms, or other blood count abnormalities) to get 1000 micrograms into the muscle or under the skin with a dose of IV folic acid 15 mg, followed by daily doses of 1000 mcg injected daily for a week with oral folic acid. Maintenance is 100-200 micrograms injected monthly.
You really, really are not getting enough if you are to get this every three months. You need more now and it needs to be aggressively given because there is ongoing damage. Getting vitamin B12 will prevent further damage from happening, but you will be left with much of the damage that has happened.
If one has one autoimmune process–such as pernicious anemia where antibodies attack the upper digestive system where B12 is absorbed, one can have a second autoimmune process like CIDP. If as the neurologist says, he thinks this neuropathy is due to B12 deficiency, you need much more aggressive treatment and if things still progress, then it might be CIDP. The first order of business is lots more B12, though.
WithHope for a cure of these diseases.