if you masturbate too much then the reason is mainly too much protein in-take and too much sex hormone production. To control hormone reduce in take of such hormone producing food and reduce protein in take. As you are growing now you must take protein but do not take more than required for your age. Excess protein is not stored as it happens with fat or carbohydrates (starch or sugar). Hence too much protein induce sexual activities.
Try reducing protein rich food and take milk only with enough carbs for a month. Milk is very important although it has high protein. Let milk be there and rest carbs. you will see that you will hardly urged to masturbate.
its alright im a female and i started masterbating at 11 and I still do it frequently. over time your mind will become preoccupied with something else and you will do it less often.
Its not so much a matter of how to stop completely but more a matter of not doing it as often. You see at your age its normal behavior everyday. As you get older it will happen less frequently. To cut back on the number of times, you'll have to change your daily routine to include more outside activities where you're with other friends and other people. My guess is you spend alot of time by yourself. Get out there with others.