I think all of the other answers have been great, but I thought of something else. Another consideration is the impact of sunlight. Are you getting enough sunlight? Are you getting enough vitamin D? Also what about your EFA ratios? You should try to be in the 1:1 to 4:1 range on omega 6 to omega 3's The brain is largely made of fat and relatively high in long-chain omega 3 fatty acids like DHA and EPA. Deficiencies in these fatty acids impact brain function in many ways, one of which can be fatigue.