Need some help.. please

Hey everyone, just wondering if anyone has experienced something similar.

I was diagnosed with coeliac disease earlier this year, and my B12 was around 400 back in April. Over the last two weeks I’ve started feeling really off again; extreme mental fatigue, brain fog, feeling spaced out/dissociated and constantly tired. I can sleep 10 hours and still wake up exhausted.

My vitamin D is currently in the low 50s and I’m supplementing. Ferritin is around 250 after an iron infusion, so that seems okay.

I had similar brain fog/dissociation earlier this year which eventually completely went away, but now it’s back and I’m wondering if my B12 could have dropped, especially with the coeliac diagnosis.
I’m going to ask for another blood test, but has anyone experienced similar symptoms or had their B12 drop significantly within a few months?