I don't think you should start dieting already.
I've done it myself at the age of 14 but it went totaly wrong because I was thinking to much about food! It's the same effect when you say to a child it may not have a candybar, it's going to take it anyway, just because they know they may not take it!
If you see donuts and you think: no I really cannot take it, you are going to take it anyway!
maybe not in the first weeks, but it's just a matter of time before you're gonna eat donuts again and then.. those pounds are back again!

it's better when you just eat healthy food, and sometimes a little bit candy or chocolate.
don't punish yourself to much! when you're happy, and don't focuss on your diet to much, you will look better and, after a few, week, skinnier!

Good luck girl!

Maybe you should start by learning the hunger signals and see if that helps!

Full feels like a warm, pleasant sensation in your solar plexus (under your rib cage and above your stomach)

Ideally, you would want to initiate a meal when you are in a state of hunger but not completely famished (a scale rating of about three), and finish a meal when you are in a state of fullness but not completely stuffed (a scale rating of approximately six).

0 3 5 7 10

0 = Starving, famished, headache
3 = Need to eat something, hunger pangs
5 = Comfortable, lightness about you
6 = Somewhat full, satisfied and content
8 = Overfull, need to loosen clothing, must sit for awhile
10 = Nauseated, vow to never eat this much again

HOPEFULLY THAT HELPS!!!!