Without knowing anything (along with my tendency to make grand, sweeping statements) I'd guess it could be one of two things: 1) fear success (and added responsibility due to said success) or 2) You're in the wrong career and (secretly?) want to change to something else. I think that's usually the root of procrastination. Just a wild guess. I mean, it sounds like you're already pretty disciplined and productive anyway, just not toward your job. It sounds like you're not motivated in that area.
OK, I'll shut up now before I offend anybody.
