Since I have chronic fatigue, I can give you a little help here. First, make sure you're B12 levels are adequate. Have the doctor test it if he hasn't recently. If low, the methylcobalamin form of B12 will help both energy and mental focus.
For energy, I also take NADH and d-ribose. For mental focus, I find that phosphatidylserine helps.
I recommend taking Dr. Braverman's test for neurotransmitters (can find it online) to see what your dominant neurotransmitter is and which one or ones might be low.