Thanks for your question. There are many different ways to classify weight. Most ways of classifying weight look at your age, weight, and height. It’s important to know that everyone is meant to be a different body size and shape, so the most useful way to know if you are at a healthy weight now is by seeing how you’ve grown (weight and height) since you were a baby. There is no “correct” weight for a certain age, only a healthy weight range for each person based on their personal growth history.
In general, teens are supposed to gain some weight as they get older to help fuel their body as it goes through puberty. To gain weight you have to take more energy in (through consuming food and drinks) than the energy you spend (through exercise or physical activity). The American Academy of Pediatrics recommends that all teens get 60 minutes (or more) of physical activity a day.
Also, if you are throwing up after eating, this can be a sign that something more serious may be going on. This can also be the reason why it may be hard to gain weight.
We recommend talking to your health care provider. They can let you know if you are at a healthy weight. They can also help determine whether there are any medical problems that are causing you to throw up after eating.