Hydration, rest and a good diet of course as a first recourse. .I have been getting pretty run down as well due to life issues and 70.3 training. I've found that adding some supplemental Glutamine in for a week or so seems to help me snap back. I was really beat last week and my throat got pretty sore, so I took it for about a week. I usually start feeling better after about 3 days on it. My recovery, energy and ,therefore, my mood improve. I don't take it regularly, but do use it when I feel I might be more depleted.
Hope you feel better soon!