Get one of those special SAD lamps if you can, and use it every morning! It really does help me, when I make the time to use it.
Also do all the usual things people recommend for any kind of depression: see your doctor/therapist, consider medication, get more exercise, journal through your feelings, stay busy, etc.
When I’m having a bad SAD spell, I find it’s almost always curable with 20 minutes in front of my lamp followed by a brisk outdoor walk until I break a sweat. The trick is gathering the will to actually do these things. If I can push through the haze of depression enough to do these small things, I will consistently feel better.
Good luck, love!