I am surprised you are all right on B12 tablets. Pernicious Anaemia (which I also have) means you cannot absorb B12 through your stomach, hence needing to bypass the stomach and have injections into the blood. Amongst other symptoms B12 deficiency can cause neurological symptoms which can mistakenly be taken for diabetes related. If you have a diagnosis of PA it is usually injections every 12 weeks for life. Metformin can eventually stop B12 from being absorbed and so do PPI's.Was on Metformin and having B12 injections quarterly. Then I ended up in hospital as an emergency with pernicious anaemia and had to have 4 litres of blood.
Now on Rybelsus (semaglutide), with daily iron supplements and B12 tablets. Much better.