Instead of 50,000IU once a month you could try 10,000IU once or even twice a week (definitely check with your doctor on this regimen) with B12 (sublingual should suffice, use better absorbing methylcobalamin form instead of cyanocobalamin) and highly bioavailable form of magnesium supplement (your fatigue is a classic sign of insufficient B12 and magnesium - see post #97 on magnesium depletion while taking large doses of Vitamin D).
Definitely run this by your doctor, so he can monitor it.
Thank you, I will. Interesting you mention the B12 and Magnesium. My daughter and I both get Migraines. I didn’t think I got them enough to warrant a visit to the Neurologist but my daughter was getting them quite frequently. She didn’t want to take a prescription so the doctor prescribed B12 and Magnesium which she says has helped a lot. Maybe a genetic thing?