How do you gain weight?Help!!

M

So I'm 5 feet and 14 years old I weigh about 80 lbs and I've tried so much stuff to gain weight but it doesn't work and people at my school have started a rumor about how I'm anorexic and I don't know what to do. I eat so much healthy food that all the time and in constantly hungry and I've never been on any kind of diet to lose weight I just don't know what to do it's going to point that people have started making rumors about me and it's all over school now.