Do people have a right to tell you that you look anorexic if you're just skinny?

I am 13 and a number of people have told me I should gain weight or that I am a stick. They don't think they say them rudely, but I feel it is insulting. If I was obese, they wouldn't have the right to tell me I was fat. I weigh 75 pounds, but am only 4 foot 10. My doctor tells me I am healthy wieght for my hieght.