Maybe what would help is a reasonable list you could write every night of the things you would like to achieve the next day. You list the tasks you want to do, but don't exaggerate by putting too many things on it.
It will be very hard in the beginning but every time you have achieved a few consecutive days of handling your tasks that are on the list well, you can give yourself a little reward.

I have quite severe depression as well, but writing down that list helps setting me little goals, even though I don't always quite achieve them.