maybe talk to your doctor if you're really worried about it, I was super skinny when I was 16 even though I was eating loads (amongst other symptoms too though lol) and they found out I had a thyroid problem 😂 It's probably nothing to worry about and you're probably perfectly healthy, like some people ARE just naturally really slim, but if it's making your self-conscious or you're feeling any other symptoms you could try seeing if your GP has any advice?