You are a healthy size/weight for your age - what happens is that you are surrounded by images of the fashion industry which demands you fit their concept of beauty and not that of nature - as you are intended to be. In other words, their fake concepts are based purely upon their own flirtation with unreality.
And if you watch too much of this, you will go insane, just like the skinny skelators on the cat-walk.
http://wwitv.com/tv_channels/b6608-Fashion-Channel-Italia.htm
This is what 'normal' people (us) look like.
https://www.google.com/search?site=&tbm=isch&source=hp&biw=1600&bih=791&q=ordinary+people&oq=ordinary+people&gs_l=img.3..0l10.2444.6312.0.9069.21.12.4.5.5.0.174.1136.9j3.12.0.msedr...0...1ac.1.61.img..0.21.1235.wOl82izF-94#tbm=isch&q=people
It's only when we observe ourselves in pictures, that we suddenly realize just how bonkers we really are.
Forget everything you've heard or read. I promise you that you are perfect as you are - do not listen to the rage of those who think otherwise - they are of that small pimpled minority who want something which they cannot have - skinny without death.