How can I control my ball in tennis? (speed, direction, etc.)?

Alright, Yahoo! Answers has helped me so far and I would like to give a thanks to all those wise and friendly people out there who gave me all the advice to help me out lately. So, now lets see who can give me some help in tennis. I've been playing tennis for three years now (currently 14) and I have always had the problem of hitting the ball too hard. Recently, I've learned to control my strength but when I'm hitting the ball like a freaking pansy, the sport bores me. So, I started trying to ask my coach for help and his advice didn't do (excuse my language) a damn thing. I've tried asking friends, family, family friends, etc. but nobody seems to know what to do (not many black people play tennis around here). Now when I hit the ball hard, it doesn't go over the fence or into the net. It just goes out of bounds. There have been times when I hit it as hard as I could and it perfectly went where I wanted to go and I won my point, but I can never do it over and over again. I practice everyday, but I'm not getting anywhere. My mom tells me to take it slow (pansy hitting) and then progress a step at a time, but (excuse my language again) that **** doesn't work for me. If you have any advice, please feel free to tell me. I really do need this..