>>1No worries, i used to be super fat myself ^.^ you say you need a coach, you could ask your parents to get you membership to one of the gyms like the YMCA.
I'm a guy by the way, 6'1" I'm currently on 200ilb on the dot, but i weighed about 245 when last school year started.
It just takes commitment and a healthy diet and you'll drop weight :)
Besides that i can't find much else to say besides find a coach or a local gym to sign up for, since it sounds like the best way for you to lose weight ^.^