Without blowing this out of proportion, I think this can also be a slight case of depression. At least, lack of motivation (perhaps from some sort of "non-joy" in your work-environment and tasks) and "there's just no point in doing it" along with your negative self-thoughts, are all part of depression as an illness.

The "I'm a complete failure"-part resonates with me, and perhaps, it could be something as simple as being so afraid of failing, that you never even try.

I don't know if this is helpful advice at all, but it might give you an idea of what you can do to help yourself (CBT for instance).