If you're naturally slim, possibly not. I would recommend eating a healthy diet and visit a nutritionist and/or a pediatrician (they're knowledgeable regarding the health of teenagers as well as children), you should be alright.
i totally get why it would worry you to look like that from the outside, but it doesnt have to mean anythings wrong on the inside
but yes does depend on if you have become like that or if its how you always were anyway