I have bipolar disorder and was seriously affected by SAD... until I got a special full spectrum lamp. I use it every day now that the days are getting shorter, and more often when there is a streak of grey days.
Any psychiatrist should be able to tell you where to get a good light near you. They are a bit expensive initially, but the bulbs last a very very very long time and the investment is worth it.
I still find some days tough (especially this time of year), but this lamp helps so much. I'd say a 100% improvement since I've started using it! Plus, make sure to get some exercise on the bad days (even a 15 minute walk), no matter how awful you feel.
Hope you feel beeter soon