When someone say "Your not skinny at all" or "Why are you so skinny, don't you eat" you should listen to them right? NO YOU SHOULDN'T!!
Body's come in all different shapes and sizes, some are curvy,box like or even look like an hourglass but every one is beautiful in their own way. There's no perfect body, everybody has their own insecurities, some may not like the way there nose is or how big their thighs are and that's fine but you don't need to hide it, you need to let it shine because that's who you are and it's not gonna change. If you want to get in shape go for it but do it for yourself, to make you feel better, not for anyone else. It's just like makeup, people think they need makeup to be beautiful, just like how you think you need to get in shape to be beautiful as well but that's not true. You are beautiful, you are strong and you shouldn't be ashamed for that.
You shouldn't waste your time telling yourself the negatives about your body because that's just dumb. So look in the mirror and say to yourself " This is who I am and I love it" So don't focus on how you want others to see you, focus on how you want to see you because you are amazing in every way