(Disclosure: horrible typist here, so apologies for any typos, etc!)

Nowhere - it's possible you could be in perimenonpause. It has many symptoms and depression can be one. Suggest getting your hormones checked. Unfortunately, many docs are not so great in this arena (even endocrinologists) so take it upon yourself to find someone good. Could be thyroid - same thing, you have to find a professional that has a reputation for really knowing their stuff.

Scotsmen - have you explored the thyroid route for your depression? And/or diet?