Why do I get so tired?

Ever since I had major surgery for a brain aneurysm 2 years ago I cannot exercise or do anything strenuous because I feel so drained and fatigued for days after. Im in my forties and I do take thyroid meds and my labs all have come back OK. Im taking different meds and my Doc does not think that they are the cause for the fatigue. I did have a CT of the chest abd and pelvis and it showed nodes around the abd. area. But still I feel so tired that I can't do much except go to work and come home. Sometimes this causes me to feel so depressed that I sometimes feel that life is too difficult for me to endure. I talk with other men my age and ask if they feel or felt this bad and if it takes this long to recover and the answer is always no. thanks for any input or ideas