Why don't I have any ambition to do anything?

I have no ambition for anything other then to find a way out going to work and sleeping. I don't have any energy to even clean the house. I am watching my world fall apart in front of me, I think it already did. I try to avoid everyone and get bugged and really stressed if thing don't go smoothly. When I do get out I try to keep my self busy so that I don't have to go home. Why am I felling this way? It has been this way for almost a year.