The pathology of agony

I was once described as precocious, now family members consider me as having the tendency to brood--to be consumed by thoughts or expectations. I find that this tendency, like many human tendencies, poses both positive and negative effects: focus and productivity at work or at home; fixation and gloom when faced with uncertainty. I've heard innumerable words of encouragement, tips on how to achieve a better outlook, or counting blessings--I might as well be considered the expert on positive living, but we all know that theory isn't always practiced. It's ironic that people come to me for advice or catharsis yet here I am feeling completely inadequate.

Can all this be reduced to something clinical? I hope not. I'm pretty sure I'm just over-analyzing things.

(I'm my own shrink.)