I'm 18 and I have a long nose with a hump. Can it be removed by gaining weight or rhinoplasty?

Weight  gain or loss will not change the shape of the nose in any meaningful manner. If you are serious about improving  the appearance of the nose you should consider seeing a board certified plastic surgeon to discuss your options and find out if you are a good candidate for treatment. 

Thank you very much for sharing your concerns with us.Through rhinoplasty we make small changes, but that is quite noticeable. After having analyzed all the info. i recommend you perform a Full Rhinoplasty, includding narrowing of the nasal base, with nasal bones treatment, and alar and triangular nasal cartilages shaping.With this procedure you get a delicate nose, better harmonize with your other facial features.Respectfully,Dr. Emmanuel Mallol Cotes.-

 The dorsal hump is composed of both bone and cartilage. There is no fat in the nose, so weight gain or loss will have no bearing on the nasal features. To remove the hump, it must be shaved down surgically with a rhinoplasty procedure. A closed rhinoplasty approach can accomplish these goals of hump removal. After the hump has been removed,osteotomies are then required to be placed in the nasal bones to narrow the bridge line. For more information and many examples, please see the  link below