aw, hun, i know the feeling...17 years old, 152 lbs.
anyway, heres my ideas.
excersise:
try going running each morning. not on a treadmill, outside. it's easier to motivate yourself if youre outside and actually GOING somewhere.
make a playlist of music to listen to while you are workign out.
try doing situps every time commercials come on during the shows you watch on TV until the commercial break is over. fills in the time, and works like a charm! =]
and also, the areas you wnat to foucus on working out most right now are probably stomach and cardio. theyre good all-over helpers.
dietary:
try deleting 3 unhealthy things from your diet completely. especially soda. soda is practically liquid candy.
everytime you go to get a serving of food, get the amount you wnat, but throw away half and eat half. this will also work very effectively.
try gettign smaller servings- its easier to limit the amount you eat if you dont have as much on your plate.
also, take smaller bites, and chew slower. you'll get full quicker.
try eliminating unneccesary snacking form your diet. only eat when you are actually hungry.
hope this helps!