I would suggest you speak with your coach about this problem. A good coach always knows how to keep his players loose and relaxed. IMHO lack of confidence is just a lack of focus.
My high school coach and this was many years ago had a little thing he would use to help us focus. The batter who had the most strikeouts in a game the following practice would have to wear a pink helmet during BP. Now you can imagine what kind of poking the player got that had to wear that pink helmet during BP at practice. It was all in good fun though.
In the dugout the guys would be poking at each other about who was going to have the honor of wearing that god awful pink helmet the next practice and coach brought it to every game LOL. Also each time you had to wear it you also had to sign your name on it. Surprisingly enough coach and the thought of that helmet kept us focused and loose at the plate.