I echo the suggestions about getting basic vitamin and mineral needs addressed. But i would caution about oversimplifying this. Vit D is pretty easy. Other stuff is not. B vit supplementation can be tricky. Also, some people might pop a few pills, not feel better, and abandon the whole nutritional aspect. What's really needed, i think, is a complete assessment of diet and nutrition. Gotta get the poisons out of the diet.

Problem with mainstream healthcare is that it seeks simplistic solutions to complex problems, like depression. Take a drug to fix your "chemicals", talk to a therapist, take a few vitamins, call it a day.