It is hard to work at any job when you are in the grips of depression, I can emphathize. What's worse is being stuck at a desk all day with the same people around all the time. You can't really blend into the woodwork or hide how you are feeling. I have been self employed and find it easier seeing different people all the time, it's easier to hide your mood.

I don't have any advice other than try to schedule frequent breaks away from your desk if possible. Can you get out a lunch time and go for a walk? Sometimes just getting away from the office environment helps.Another option is FMLA leave until you are feeling better.

I hope things improve with you.