Eat less sugar. Fast food and sodas give you a sugar high addiction. You'll start feeling cranky, headachey, hungry and tired when your sugar levels are falling from high to normal levels, not to mention fasting levels.
At least that did the trick for me. I'm feeling more stably energetic than I did before now that I've cut down on processed sugars dramatically. Since candy and other garbage is no no, I've lost a lot of weight too, which certainly helps depression too.