--that B12 levels can come out artificially inflated on a serologic test if you have been taking oral supplements.

But the fact that even with supplements you "only" came out at 959--not a very high level for someone who supplements (I do 1000 micrograms of B12 three times a week, and also take a general B supplement with 125micrograms of B12 each day, and my B12 levels generally measure in the 1500-1800 range--enough so that I have to explain this to doctors) indicates to me that you were VERY low to start with (as your previous tests seem to indicate) and/or you are still perhaps having some trouble absorbing as much B12 from the supplements as you could.

The theory behind massive oral B12 dosing is that you can passively absorb a few percent of a very large dose and that will be enough to build stores. A daily 1000 microgram (1 milligram) dose can normally provide somewhere around 10-30mcg of B12 even if you are passively absorbing at 1-3%, which are figures often given. Since the daily minimum requirement of B12 is somewhere around 2-8mcg, this is enough to start rebuilding supply. But, there are many things that can interfere with absorption. Certainly, a history of PPI or H2 antagonists can inhibit absorption--acid is needed to break B12 out of foodstuffs and also for fullest absorption even from supplements. And, one should take one's B12 apart from anything else, as it is very easy for the cobalamin molecule, which is the largest molecule our body regularly uses, to be complexed up chemically if one takes it with food or other supplements (two hours after eating or one hour before is likely a good idea).

I also suspect those cholesterol binding meds were not doing your nutrient absorption ability any favors.

The neurologic symptoms, and many others, could certainly be explained by the low B12 levels, and it's likely you may be low in other vitamins/minerals as well, given your history. I'd definitely have your magnesium, calcium, and D3 levels checked as well--the iron you already know about. (Iron deficiency is not unusual in adult women who have heavy menses, but iron and B12 deficient people should also be worked up for irritable bowel syndrome, Crohn's and particularly Celiac.)