I can relate to these feelings. All I can say is to hang in there. I know how rough it is, and how worthless I have felt when I've been in these states. Do you have any support? Maybe someone in your family? You clearly express yourself well in writing -- do you journal, or express your feelings in some other creative way? Having support and a creative outlet helps me. Sometimes also distraction -- crossword puzzles for whatever reason work for me, even in the midst of a lasting depression. Aromatherapy, with nice candles. Popping bubble wrap.

Sometimes with depression, it's partially about waiting it out, and partially about tricking your mind by doing other things. Work is a great distraction for me. Is it for you? It's odd how I can be so completely depressed, yet still perform well at work. You might be a better teacher than you realize.