I'm taking mb12 but don't have b12 deficiency

My serum b12 levels are in 700's and my MMA test came back normal. I've been experiencing a constant fatigue symptoms, blurry vision, unbalanced glucose levels (going from 165 after eating sugar or simple carbs down to 60 in 2-3 hours), joint/muscle pain, brain fog, and other chronic symptoms. I had every test known to a medical western doctor, and all seems to come back normal. The only thing that keeps on showing is low Vitamin D.

I have 2 copies of A1298C MTHFR mutation and 2 pregnancy losses. I decided to purchase Methylcobalamin B12 and am taking it everyday in 2,500 mcg doses. It does give me more energy, but I'm still feeling fatigued.

Also, when I tried a small dose of methylfolate, I had several adverse reaction (heart palpitations, sweating, irritability, and generally feeling not well) after being on it for about 4 days.

My questions are: should I continue taking mb12 even though my test results don't show any deficiency? What would be a good dose to take to relieve fatigue that has been lingering for over 6 years? For how long should I stay on it? Would it be wise to add methylfolate despite the side effects?

Thank you so very much for your help.