Read something interesting today. Don't remember the exact words, but the gist was that you can't necessarily tell an introvert from an extrovert by how they behave around people: an introvert can be plenty talkative when need be. What makes the difference is where they recharge their 'batteries'...for the extrovert, being around people does the trick, while the true introvert needs time alone.
By this definition, I'm an introvert, always have been. I remember being a little kid and going voluntarily to my room to read quietly for a while every day after school. Even now, as outgoing as I generally am, I hit a threshold of contact with people after which I need to go be by myself for a while...there's only so much I can take even of people I genuinely love before I need a few minutes of quiet to regroup. The really funny thing is that I decided to marry Himself in part because he's one of the few people I've ever known that I don't need to 'escape' from...maybe because he's an introvert too and can just sit quietly with me!