How can I use nutrition to improve my mood?

[GBG]

I'd like to treat what may be mild, chronic depression nutritionally. I can't take herbals, I'm allergic to them. I believe I heard something about fish oil good for it, and also b-complex vitamins. I already take some Centrum once in a while. Would that plus eating a healthy, varied diet be enough? Would if be helpful if I go buy a bottle of fish oil and b-complex tablets?I want to give this a shot before I go the "medical treatment" route because it's not serious and it may be all I need.