Listen to angelajohn
I suggest you not to have supplement ,eat natural foods and get your body fit as its possible having healthy food.
You are 15 years old, and unless a doctor finds a deficiency in your health, DO NOT TAKE any supplements.
You will get fat sooner or later, but you will mess with your body and health if you ":pushed" it.
Eat food in their natural status. If you need omega 3, eat wild catch fish
, and enjoy it.
The web is full of references with natural alternatives, and if you love yourself, don't use artificial made supplements.
These supplements are better needed by people who is older from 30 and up, specially the ones who have destroyed their organisms with poor eating habits, lack of exercise, suffered diseases, etc.
You are young, you don't need supplements.