How are things at home? If you're having a bad time at work but your home life is great, you probably handle things at work better. If it's bad in both places, that's really difficult!
Are you eating, sleeping, and getting exercise? All those things help you cope with difficult times. Also, what about friends? Socializing with positive people can lift you up. I go to church, and it really feeds my soul. Maybe that would help. How long has this been going on?
Hang in there! Hope everything gets better soon. Keep us informed.