Your story rings so familiar to many I'm sure, I know it does me. When I was around your age I used to get picked on both at school and by my family for being too skinny. Whether or not it was because of this or something else I too used to come home and eat a bucket load of crap, which was fine when I was training every afternoon, but not so fine after I stopped training. I eventually developed a life long bad habbit of eating whatever I wanted when ever I wanted.
Its great you recognise this so early, give yourself heaps of gold stars for that.
If you can, try writing down what you eat, and why, were you hungry, bored, cheesed off, happy, sad etc. Get to know why you eat and when. It will help you develop strategies to get around it.
For example, do you eat when you get home because you are bored, if so, what else could you do to not be bored. Do you eat the junk food because its there... can you ask the parentals to not have it in the house. Are you eating when you are cheesed of or feeling down, try finding ways to change how you feel, music, hobby, talking to a friend etc.
Knowing you are going to come home bored and eat, have something ready to go when you get in, something more good for you than ice creams etc.
Good luck bro, keep in touch, we'll be thre for you.