Theater has a way of bringing out the confidence in people. It's a world full of openness, honesty, and people who are trying to work through one personal issue or another. And in performance, most people find freedom - because you aren't performing as yourself. You're channeling an entirely different person, with entirely different neuroses, so in essence, you can choose to play out your own stuff through a character that isn't you. It frees you from those things that bind you - like shyness - because you get to set it up, push it out, and spit on it. You always come out victorious.
Or, at least, that's always how I've seen it. That's why so many people enjoy it. Well, it's one of the reasons.
Acting lessons, though, are totally different than, say, a theater class. If you are in a position to join a community or school play, even if it's just as an extra body on stage, or if there are group acting classes - take them. I do think you'll get good things out of them.
I hope you choose to.
Stage actor (professional, fringe and school) - 12 years. Formerly an utterly insecure and socially inept dorkus. :)