It sounds to me like you have seasonal affective disorder [SAD]. There's an extremely simple, safe treatment for it with zero side-effects--full spectrum lightbulbs in all your lights. And then keep the lights on all day and you'll be amazed at how much better you feel. We switched all our lightbulbs to full spectrum, and keep a lot of lights on for our dog who has retinal degeneration and can't see in the dark. It dawned me the other day that the light has really helped my mood this fall.

Low melatonin is also associated with SAD so you might try that. Start with a low dose, and go from there.

Another thing that's really helped me this year [I always end up depressed by mid-September as I live so far north] is taking nascent iodine. I just started taking this earlier this year, and between it and the lights, I haven't been at all depressed this fall which is amazing.

Here's a video on iodine: