How to make my metabolism fast again, recovering bulimic?

i've been battling with bulimia since june or july of last year (NOT severe bulimia at all). in the beginning of me stopping, i didn't gain weight. now i see that i am starting to gain weight this time when i stopped in May, and i went to my cousins and his mom fed us a lot of food, and when i came home i weighed myself and i gained weight so i binged this morning and purged. my weight fluctuates like everyone else, but it never goes down and i gain weight easy. how can i make my metabolism fast again so i won't be afraid of weight gain as much? im only 16, almost 16.