Happy birthday OP. Even though in reality it wasn’t, I hope these Birthday wishes from internet strangers make you feel at least a little loved by all of us. I’m sorry you’re being treated like that by your family of all people.

Don’t allow yourself to feel fat shamed, please. It’s your own opinion that matters. If you want to change, then safely do so, if you don’t then all is well, no one else’s opinion matters in reality. I guarantee you most others won’t think the same as your family too.

I promise you things will get better. As soon as you’re old enough, leave their horrible company and make yourself happy with people who love you in person and treat you well, and find what makes you happy and do it.

Wishing you many more happier birthdays for the future OP, things will get better.