This makes me think back to psychology class. There's a disorder called SAD. Seasonal Affective Disorder. It's basically what you describe. I remember the professor saying that's the easiest to cure. Use a sunlamp (not sure where to buy one) about 30 min to an hr. a day during your seasons of depression. Don't know if this helps or not, but it couldn't hurt to try. Here's hoping you feel better soon.