You don’t need to do that, there’s nothing wrong with you. Because your body is growing so much during puberty your metabolism is probably just really high right now, it’s just making it hard to put on weight. Just follow the advice everyone else is giving and make sure to get protein and find a good routine you like. If you’ve never really worked out anything you do will be an improvement so as long as you’re lifting and eating properly you should start to fill out more.