I would suggest you get the following investigations like a complete blood picture, thyroid
function test, serum electrolytes (sodium, potassium), calcium levels, Vitamin B12
levels done as anaemia, thyroid abnormalities, altered electrolytes, Vit B12 defeciency can present with fatigue
. I'm assuming that his blood sugars, lipid profile
, liver function test and kidney function test have already been done.
Hope this helps.
Dr. Divya Kuttikrishnan