B12 deficiency, b12 shots regularly, but b12 continues to drop dramatically between each shot.. underlying cause? (no anemia or other issues)

Likely Many Misleads: B12 deficiency takes ~2 decades (eventually pernicious anemia) to be obvious. Like all vitamins, only a helper molecule for larger/more-complex protein enzymes; very widely present in nearly all foods (humans have have lost typically a single gene needed to make the vitamin). If being injected, likely not B12 or dose so low as to be irrelevant; check B12 before ; a few days after injection.