Please help me. weight problem.?

i am a female. i am 5'7 and i weigh 180. i no that i am overweight, but i am not THAT overweight. i try all the time to stop eating bad food and to exercise. i play tennis 2 hours on friday, but thats it. i do way too much hw. i am an over achiever, just not in weight. i have a bowl of cereal for breakfast, a sandwich and granola bar for lunch, and usually meat, salad, veggies, rice...along those lines for dinner. how do i stop myself from getting snacks from the snack machine at school, and how do i eat better. i am planning on walking/running on my dreadmill for 20 minutes a day (thats all i have time for) and then doing exercise with friends on weekends, but i need help with food. i have HUGE sweet tooth and i will do anything to stop. i have thought about wearing normal sized shirts and looking attractive, i have thought about guys looking at me and liking me. but it didnt work. i like the way i am but i want to LOVE who i am and i don't please tell me how to loose weight.