I am 5'8 or 5'9 and i am 19 years old and i weigh only 116 pounds. is this considered underweight? what can i do to gain weight, no matter what i do i

See Dr., then eat...: If one is truly underweight (based on height, family background, and body type), a Dr. can check for a hormonal, digestive, or other disorder. If no medical cause is found, then one can add weight by eating more calories of nutritious foods (such as egg white, chicken breast, salmon; and olive oil, peanuts, almonds, tofu,...). Taking a daily multivitamin is fine to do. Some exercise is good too.