Buy some supplements that contain Vitamin D and Iron. Most people are deficient and it affects their mood. I got some meal replacements that basically contain everything and it's kept me in good spirits while everything is going to shit. I should be depressed, but I'm not.

EDIT: Iodine too. The over-the-counter stuff is called "kelp" and the reason they don't put it in multivitamins is because it metabolizes into a substance that in excess will give you gout. Iodine is hard to get from your diet so having supplements every now and then is important.