The problem stems back to low stomach acid. In your case, low stomach acid is due to age, stress and an autoimmune disease. My mother's symptoms of low stomach acid were VERY long including acid reflux/GERD, high blood pressure, fungal infections, low vitamin B12, depression, anxiety...
She now takes betaine HCL with pepsin supplements and digestive enzyme supplements with excellent results.
Just to add, high vitamin B12 in the absence of supplementation is a red flag for functional vitamin B12 deficiency. Check homocysteine levels (levels rise due to low levels of B12, folate, B6).
"Studies indicate that people with homocysteine values greater than 8.5 µmol/L are at increased risk of atherosclerosis,10 heart attack,11 and stroke.12" - Life Extension -
Is Homocysteine Making You Sick?.