While we may not be pros with depression, or Seasonal Affective Disorder (SAD),
etc., your post has triggered some great advice to seek professional help. So in
a way, it's a blessing in disguise .
While the topic is too often seen as a weakness among the Testosterone Gang, it
is real and has real impact on not just you, but others, as well. Good on you for
being honest with yourself, and asking for help/advice.
Now go have a talk with your doctor about it. S/he can help.