methyl B12 dosage

Hello,

Via a blood test, I discovered I had borderline low B12 (what led me to the Dr.in the first place is a long story..but was having chronic low immunity to viruses, flu & repeated shingles outbreaks.)
The Dr prescribed b12 injections every 2 months & follow up blood work in 6mths. (I had been on a very low meat & dairy eating regimen for almost 2 years prior to the blood work).

In the interim I was at an allergist for an inner ear issue & mentioned the low B12. Thu Dr. Suggested I take methylB12 by jarrow 5000 mcg chewable.

As suggested I quartered each lozenge & currently take 2 quarters (= half a lozenge, assuming it's 2500mcg). I was feeling great, but the last few days have been feeling sluggish & tired again. I. scheduled for my 2nd b12 injection tomorrow....are the injections necessary? And should I increase the methylb12 intake for a little? Just want to make sure it's safe? And lastly,if I am pregnant it would be very early on...is it safe to take methyl b12 at this high dose when pregnant?

Thank you for your time.