Im 14 and i feel fat all the time and i wanna lose weight and have a flat tummy !

Okay, so first of all, work on your self-esteem, because it seems you're negatively-reinforcing yourself trying to break yourself down to make some ideal for yourself(that doesn't work, you build up to an ideal, not tear down to one).

Secondly, unless we know your height, we don't have a clue how fit, or not fit you are.

Since your 14, try and play a sports, or good physical activity to tone-up, and don't over-eat, you shouldn't mess with your food to much, just eat right, and don't overeat. That should create a good balance for any 14 year old.

Tips to boost your self-confidence:
http://zenhabits.net/25-killer-actions-t…

If this works for you and you want to commit to it, start counting calories. Set yourself a limit for each day, cook for yourself (no fast food or instant food) and find a lot of healthy low-carb foods that you like. this will help you substitute fatty food or sweets.
the key is to stay within your calorie limit, so that you don't have setbacks and become frustrated.
also of course it will help if you do some sports.
good luck (: