I have tried to stop drinking soda and coffee. Right now, about all I drink is ice tea, gatorade G2, and water.
I've drank soda, coke, juice and all that crap extensively all my life and I weighed 132 pounds (59 kg) in June. Keep in mind that I'm 6'2'' (1.90m). I now weigh 143 pounds (65 kg).
Whoa, buddy. Wait 'til you're in your twenties and that teenage metabolism no longer applies...
I seriously doubt my skinnyness comes from being a teenager, seeing all the fat people of my age I know.
Besides, I exercise quite heavily to fix my scoliosis so being fit shouldn't be a problem in the future.