Pat on the back NS for a mature thread, very good. Haha. I've gone through drawn out phases of introversion/extroversion in my life depending on changing circumstances. At heart I crave social interaction, yet there has to be solid time to myself here and there to sort of...come back to myself.
On confidence: Basically from long time happy ski bums and other older, wiser friends, I've found confidence to be this...
Not giving a FUCK (about negative criticism), living WILDY, while keeping yourself in CHECK, and practicing ENTHUSIAM.
The next time you open your mouth to criticize, whine, or complain, close it back shut, until someone else speaks instead. Seriously, do it the next time you itch to bitch! Negative thinking carries a vibe with it that affects others around you, making them more likely to think negatively, bringing the mood down. Enthusiasm is like magic, and it draws people towards you. Learn to be stoked, all of the time.