Welcome to the depression forum. It seems strange that a surgery on your knee would cause you to have depression, but stranger things have happened before. It is a shock to your body and it is hard to say how the body is going to react. In either case, if life is this difficult for you, I would suggerst seeing a counselor. Or talk to your primary care physician. It does sound like you could be depressed.
Has anything other than the surgery been going on? Are you happy and fullfilled with your life as it is? If not, what in particular are you not happy with (obviously other than the down feeling that you have been having)?
I hope that you figure out what is going on with you. It isn't right to be unfullfilled with life. You sound like you are young, so you have a lot of days ahead of you. They should be good ones. Keep posting. And again, welcome to the forum.
Oh, you must of hit "submit" twice as you double posted, I deleted one...
Moderator-Depression and fibromyalgia
fibromyalgia, Chronic fatigue, depression, allergies