Many parents, especially older generation don't understand mental illnesses and it's pretty terrible for the children. They aren't educated enough, and they are not always right. Keep that in mind .
Those are symptoms of anorexia. Anorexia is not exactly the point when the person is thin and frail, but it is a mental disorder where you want to be skinny and frail, and obsess over it.
You should go to your school counselor to talk about it, and there's this www.nationaleatingdisorders.org/help-support/contact-helplin online resource (there's a number to call too, if you want). Your counselor is not allowed to share your private info with the other kids. But if you want, they can talk to your parents and then your parents can be educated on the eating disorder.