How can I stop mindlessly snacking ?

I find my self always snacking . I come home from school( I am 14 btw) and go straight to the kitchen . I have a big sweet tooth too . My dad always buy sweets & snacks . I cant stop him from doing that . I dont have the greatest will power as you can tell . & I am active but I cant lose wheight because i am always mindlessly snacking . Any Ideas ?