SUBREDDIT: r/self
TITLE: Reddit, I need some advice on"letting go" and living in the moment.
POST: This has been controlling my personal life for way too long now, and I'm ready to change. I feel as though I am not a very serious person at heart, but I am terrible at communicating this. I have been told I looked pissed off when I am content. I just want to "go with the flow" of things so to speak. The worst part- all my friends are outgoing,funny people and then there is me...it's like I have a mental block or something, I can identify my problem but haven't overcome it yet. I feel as though my life is filled with interesting events, but personally I lack the confidence or mentality to uphold an upbeat personality. I consider myself a good looking guy, but I struggle with girls because of this deficiency.

I know I can't be the only one who struggles with this. Any advice would be appreciated!
TL;DR: 
Help me "go with the flow" of things to avoid a lifetime of sitting on the sidelines while everyone around me has fun.