I have struggled through this, myself, and all I can say is, art makes me happy, or at least less UNHAPPY when things are dark.
It may be that you are seeing writing as a chore or as a feat to be accomplished. I am not a therapist, I am not qualified to speak on depression. But I do know that I often found that when I started writing something I thought of as a PLEASURE, rather than a mountain that needed climbing, then making art became part of the cure, part of the therapy, and not just another thing to beat myself up about.
So, maybe go write something fun, for yourself, not for any other purpose than it makes you happy. I don’t care if it’s fanfic, tumblr posts, erotica, comedy, biography, just SOMETHING to put those words up and on their feet.
If you think of writing the same way you might think of a job, or some other dreadful burden, that won’t help, I suspect. But almost EVERYONE can write the prose version of a doodle, or a quick sketch, and sometimes, that makes us far happier than we expect.
Just a thought. Good luck!