Dude, that is one hell of a question. I think at some point we all go through this, well at least I know I have, and my friends have as well.
I have come to the conclusion that I will never be an astronaut, a race car driver or a fireman, the three things I have wanted to do since I was a child. Am I happy with my career? No, not at all, however it does provide me with an income to do the things that I enjoy doing. I have taken the approach now that I work to live, not live to work. As long as I keep thinking that, my job is bearable and I can continue concentrating on my hobbies and my kids, (the two things that do give me joy). This is what gets me through the day.
As far as not wanting to do anything, what do you mean? When I was at the height of my depression, if there was a million dollars on the table beside me, it would have been too difficult to reach over and grab it. Maybe a change of anti's is in need? Maybe they have to be piggy backed with something else? I don't know.
What does make you happy? Family, friends, wood working, comic books, photography, painting? It really doesn't matter as long as you can use something to take your mind off your problems. I myself light a pipe and go hiking; sometimes for hours, with nowhere in particular to go. It allows my mind to wander freely, and with the added exercise, sometimes things come to light.
I wish I could be more help, good luck. If you wish to chat, PM me, I have been there.