Exercise is probably the best, but I rarely can get myself to do this... Another alternative, maybe a little easier, is to make sure to eat well--fruits, veggies, no unhealthy/fried snacks, etc. Essentially foods high in protein and vitamins. Hard-boiled eggs in the morning, for example. Taking a long, hot shower (with some good-smelling shower gel or lotion afterward) when I want to take an afternoon nap is helpful.

Good luck. Please know that you are not alone and it will get better.