Welcome to NeuroTalk...
I think you are going in the right direction, but you could go faster and more successfully perhaps.
I'd raise to 5mg tablet daily of methylcobalamin on an EMPTY stomach and get that blood level over 1000.
Not much is absorbed under the tongue, and most is swallowed in the saliva. To be absorbed in the intestine you cannot have food present, as this will act like a sponge and create problems.
So empty stomach is important. Don't eat for 1 hr after.
I am leaving on vacation tomorrow, but you can read up on B12, and why methylcobalamin is better here:
Stores locally typically do not have it...but that is slowly changing. Most of us use iherb.com, Puritan's pride or Swanson's online. It will work out to pennies a day.
Depending on how long you have been low, will determine how fast you improve. Long term damage takes time to heal.
So it is difficult to predict how long you will take to feel better.