Hi emma82,
my wife gets SAD and has been on some ADs for < 6 months, but she is having problems coming off and having to come off more slowly.
When she first came off and before the withdrawal problems I persuaded her to go to a nutritionist who got her eating a lot more protein and less carbs.
She felt the benefits of the diet pretty quick (also felt the effects of coming off the ADs pretty quick).
So hopefully you will see similar benefits.
For the SAD as well maybe you should find something to do in the dark that you look forward to, like night riding maybe. Then you have something to look forward to as the nights close in.