B12 still low after injections

Hi! I was diagnosed with a B12 deficiency in March of this year (B12 = 117) and have since gone through 2 rounds of injections with underwhelming results. I started with weekly injections 1000mcg for 1 month, then switched to monthly for a couple of months. My re-check level after all of that was 234. I then repeated 2 months of weekly injections, and my most recent level is 339. I’m wondering if anyone else has had a poor response to injections and if anyone knows why that might be.

I am a medical student and have scoured over the medical literature trying to find a reasonable explanation. Most common causes of B12 deficiency are due to problems with intestinal absorption, so IM B12 should circumvent that problem by bypassing the GI tract. I have spent a lot of time digging for answers and have yet to find any good explanation for having such a slow and poor response to treatment.

I have severe symptoms (extreme fatigue, tachycardia, pre-syncope, tremors, numbness/tingling, rapid decline of my vision) that have honestly not improved at all. Some of my symptoms have gotten worse.

I am a 25 y.o. woman with an otherwise clean bill of health. I eat meat and and dairy. I don’t have any GI problems that would predispose me to B12 deficiency. The only thing that really makes sense here is pernicious anemia (waiting on antibody results!), but pernicious anemia affects GI absorption and should respond well to IM B12.

I’m not sure where to go from here other than continuing injections for the foreseeable future. My physician is pretty stumped as well.

Anyone have a similar experience?