I'm sorry but...again....activity level question

Hi, I have some confusion about my activity level. I'm a 16 years old student who live in a dorm on the 3rd floor. I walk to the building across the road for each class, each class is on the different floor. I walk up and down my dorm at least 5-6 times a day. Every friday, I always do some activities.....1 hour of walking for grocery shopping and usually either go to run on treadmill for 30 minutes or go out somewhere. On Saturday and Sunday, walk/run 30-45 minutes each day plus some weight lifting and crunches and all the abs work out. Sometimes, when I'm in the room alone, I would dance around for like 30 minutes.....(it's kinda embarrassing, I know).

I know I should play some sports but I have a lot of study (my junior year in high school), besides, I have to do swimming in the upcoming season so I will be very active there. 

When I was in Thailand, I walk a lot (mostly like when you walk in New York, a lot of things to shop and look around) so I can eat whatever I want (not cookies everyday) and not gaining any weight. BUT now, I have to be VERY careful about what I eat. I eat well until after 3 or 4 in the afternoon..I would snack on fruits and nuts nonstop....sometimes cereal or some sort of backed snacks!!!! I would ended up 1500 calories or almost 2000 calories everyday for the past month!!!! UGH!!!! I'm frustrated!! I can feel my clothes are a little tighter. 

What do you guys think my activities level are so I can adjust how much I should eat. (I know I should listen to my body but I can binge big time and eat nonstop because I don't really know the word full anymore so...)

Thanks!