Thank you for posting your query.
There are three common causes of low vitamin b12:
1. Vegetarian diet- as most of the good sources of vitamin B12 are non-vegetarian, so people taking pure vegetarian food may have low levels of vitamin B12.
2. Poor absorption of vitamin B12- due to antibodies
against parietal cells or intrinsic fator (which is negative in your case).
3. Malabsoption syndromes- where there is poor absorption of all nutrients including protein, carbohydrate
Please consult a gastroenterologist
Wishing you good health,
Dr Sudhir Kumar MD DM