I have found you email in Junk, which I bever check, also I have found others in Junk LOL.
Right.....it I remember correctly, you did have Covid and you have had quite severe long Covid symptoms in which case, you will have to wait and see if these symptoms of which you are now experiencing, improve or not.
Time will tell.
If I have the wrong end of the stick, then please ignore my comments.
I cannot see any point in repeating your B12 although I suppose a FBC may well allay your anxieties.
My other piece of advice is perhaps to consult a Neurologist, although your symptoms would fit in with long Covid.