If he really is 15 yrs old......
Inquest,
I can see that the coach pissed you off. Take that motivation and let it burn in you and go lift. Lift, lift, lift till you are at least 19-20. Educate yourself as much as you can and STOP eating fast food. That stuff is more expensive than anything else.
You will get bigger, you will see. But it takes time. No other coach will say 'no' to you in the future. You are only 15, you have all of highschool and college to come back bigger AND better. Those will be the REAL years to be playing. It is OK to be mad, just use it to your advantage and don't do anything rash.
Rash= To do something quickly without thinking. To make mistakes by reacting to your emotions.