I am 16, a girl and I cannot gain weight. Before, I didnt really care that I was too skinny, I am naturally skinny and eat whatever I want when I want. Now I exercise in sports and still eat whatever, but drink mostly water and milk. I dont like being boney, I dont think its attractive, nor does anyone else and some people even think I am anorexic. I'm 5'8 and weigh 115 pounds. What can I do to gain weight?
Since you're doing sports, my advice is to simply focus on improvement at your favourite sport.
That requires training (practices, strength training, etc.), and eating the right type and amount of food to support that training.
It will all just balance out. You might just be in a skinny phase right now (but, 5'8", 115lbs seems pretty normal to me). But, who cares anyway. As long as you are making progress with your training, feeling energetic, and improving at your sport, you're eating enough.
If you weren't eating enough, you'd be stalling in your progress, not have energy to play, and you'd be easily tired.
The key is good nutrition, growth-promoting exercise and a healthy attitude.
A healthy diet of minimally-processed food consisting of wholegrains, vegetables and if you eat meat, lean meats will help your body grow. I'd strongly suggest staying away from refined sugars, especially soda, as these can be quite adictive - despite being an easy source of calories they can be habit forming. Of note, you are still young and going through puberty, so your body is going to require more food and rest than normal, so ensure you eat well. Of note, it is very difficult to over-eat on vegetables and whole grains as they are high in fibre, so feel free to reach for a second of vegetables at dinner.
If you wish to gain weight in a healthy manner, following a weight training program will encourage muscle growth rather than fat accumulation. Contrary to popular belief, gaining large amounts of muscle mass is quite difficult and has large bodies of science behind it. Rather than make you look like Arnold Schwarzenegger, when done properly weight-training will help fill out your form and will improve your ability to do day to day activites. As a matter of fact, (accounting for slight crude anatomical differences between men and woman) many major muscles have connections around either the hips or the chest and upper back, so that a good weight-training program often helps to accentuate the hourglass figure in women or the classic 'V' shape in men. In most cases, because of the differences in musclular potential and the anatomy of the hips between sexes, the same program can have wildly different results for men and women.
There are many question on this board about different weight-training programs, so have a look and if you can't find one that meets your needs or equipment you have access to, ask another question specifically on this matter.
The last factor to take into account is understanding why you want to gain (or lose or maintain) weight as time goes on. What other people think is attractive varies in time, and where you are, what the time of day is, or what other celebrities look like. Rather than focus on what others find attractive, focus on how you want to look, and more importantly how you want to feel and what you want to achieve. Look at sports and exercise as a hobby, an activity you enjoy in and of itself, rather than as a chore that is a means to an end. Strength-training, cycling, rock climbing, teams sports or running will all make you healthier and stronger in their own ways, so pick something you enjoy because you enjoy it, not because you want to look a particular way.
Given your age, weight and sex I'd suggest against using a food tracker or constant weigh-ins if people are already concerned about potential anorexia - at least until you have spoken with your parent's or caregivers and adviced why you are weighing yourself.
Let me start by stating the obvious, you are eating to little. If you are not gaining weight you will need to increase your caloric intake and what those calories consist of could depend on your fitness goal somewhat.
NOTE: For most people this is a temporary phase in that age group. Some will be very skinny and some somewhat on the heavier side. This does not mean you should simply "see what happens" and your age is a perfect one for getting going on correct nutrition and good training. You body, generally, will respond very quickly to changes in diet and training. See this as an opportunity, I know I wish I had!
Here is a weight gain food list for bulking up:
These are all commonly known healthy fats.
Get older. You are 16. Your height and weight are very normal. I wouldn't "try" to gain weight now. Let things come naturally. If you are lifting weights or playing sports your body will adapt to what it needs to do.
In 5-6 years when your metabolism slows down a little and you have less time for activities you will be on here asking how to lose weight... And some guys like boney girls.