One reason he may seem disinterested is that he does not know how to help you. He is probably somewhat frustrated as well, although not as much as you are. This is a frustrating illness, so welcome to the club, I guess. You have found a good forum.

If you have any doubt about your B12 level, we normally say you can safely take 1000 mcg per day methylcobalamin, and it's fairly inexpensive. Some people take 5000 mcg per day.
Ron