Before you beat yourself up for what you've done, the paths not taken, the opportunities missed, remember this:
Because of the lessons of yesterday, you know more today.
And as we all know from those time travel movies, changing one thing -- no matter how insignificant -- can change the you of now. So, stop looking back, and enjoy the now.
If you're really not happy with where you are, rather than "what if"ing or "should"ing yourself, take action. Take a class or two to learn new skills. Rewrite your resume. Just do something. (Complaining doesn't count!)
Ciao Bella!
Eden!