Try some melatonin before bed as suggested above.
I also suggest trying one of these out:
http://www.amazon.com/Philips-goLITE...pr_product_top (read some of the reviews)
You could be suffering from SAD (seasonal affective disorder) caused by the shorter days in the winter.
I've been using the light for a while now, it definitely helped me get back to normal. I was a zombie for about a month - until I tried this.