Welcome to the forum,
Things are never as bad as they seem. I have been doing a self help depression therapy course online which I am finding helpful. It makes me think more positively - and i try to think before I feel - which helps as well. The program was written by ANU, the national university in Canberra, Australia. It's called MoodGym, and is very worthwhile. So many of the statements in your post reminded me of the warped thoughts i was reading about today.
I'm not sure if I'm allowed to mention this program. If not, I won't be offended if a moderator removes the name.
Hope things get better. Seek some medical advice - it sounds as though you can't resolve this on your own.