I'm having some serious trouble picking up the pitch as a hitter?

I'm a 15 year old baseball player. I hit great in batting practice, but when it gets to the game, I have trouble recognizing the pitch in an at-bat like I do in BP. Also, my mechanics often become poor in an at-bat. I was wondering if anyone had any tricks that helped them in the past to pick up the pitch and decide to swing quicker.