Hey there. Sounds like it's been pretty rough for quite a while D: Is talking to your parents about this an option? Your mom and dad really sound like they love you and I bet they would hate to know that you've been feeling this bad all by yourself. I would start with just letting a few people you really trust know, I bet you'd be surprised with how much they want to help.
Learning to love yourself is a very long journey and it doesn't always go as planned. I will say that on some days I still dislike how I look like but I've gone a long why from where I've been. On most days now I look in the mirror and like what I see. Now, I'm not skinny by any means but I like the curves on my body. I am built more like a fighter than my sister who's figure is pretty like a ballerina. But I like being soft and gentle and grounded and strong. Plus, I can give way better hugs than a lot of the scrawny friends I know haha.
The most important thing that you should be concerned with is your health. Because when you're healthy you'll start feeling better too. It's great that you exercise but be sure to do it gently because running yourself into the ground will not make you beautiful, it will make you tired and exhausted. Give your body the right nutrients and it'll grow even more beautiful than you are already. Please don't compare yourself to other girls though. You are beautiful for you and you house a soul that is loving and kind and so very excited to grow up. So please treat yourself well. Unfortunately, this isn't a lesson that can be told to you but something you must accept yourself. But until you can love yourself please be gentle to yourself