Your endocrinologist is concientious. I don't have an answer for you, but I'ld like to know that myself. So I'll follow here.

I take vit D 1000 units twice a day. I was told by a doctor years ago to do that. I have no idea what my blood level is.

This might be a bit off topic, but low iron reserves can also cause fatigue. A lot of us are walking around iron deficient. Even when there is no anemia, there can be iron deficiency. The blood test for that is "ferritin," which should be over 100. Doctors don't often check that.

I hope you feel better.