Why is my skin getting worse and worse?

I'm 17 and i have very pimply face, scalp, and back. I tryed everthing. When i was younger, my skin used to be so beautiful and shiny. Even one year ago my skin was nice than now and i used to eat more junk food than now and was also skinnier!! How is this even possible, when i was a kid i used to eat so much **** and be skinny, now i eat healthy and am overweight. Welcome to becoming an adult or what?