I have a healthy lunch and recess every day with only one treat. But then afterwards..?

Afterwards at home (after school) I always snack on those mini packets of maltesers, or like 5 tv snacks at the most on top of that. Is this bad?? Because i really want to stop. How do I get out of the habit of being addicted to snacking afterwards, when I know I pack enough for lunch. I think it's just a habit. I just want to stop snacking so much, I'm not fat but I worry about becoming fat now that I snack a lot. How many treats should a 15 year old girl be eating in like a week and what are the better ones?