Sounds to me like you have depression. I say this because I suffer from depression, and your sentiments echo mine at some of my lower points. Try the symptom checklist at
beyondblue: the national depression initiative and talk to your doctor. There are so many people that don't know they have depression.
Just knowing that's what's behind it helped me alot. It's easier to jump a hurdle if you know it's there to start with. Hopefully this is helpful.