Re: what does 16.8 bmi mean?
Thing is, BMI isn't enough all by itself to tell you whether or not your weight is right for you. Normal BMI is a little lower for short people, and it can vary a lot depending on your bone structure and muscle mass. It is possible to have a BMI as low as yours and be healthy, I know at least one such person.
As a woman, if you are at least 20, you should have a little bit of "pinchable" fat on you somewhere. Absent or infrequent periods is also evidence of being too thin for your body. If you are still a teen, you might still be putting on mass.
Try to eat more high-calorie healthy foods, such as nuts, dried fruit, lean meat or fish, whole-grain bread, and dairy products with fat left in. This will also help your weight training build muscle.
Some people are just naturally small. Do you have very fine bones, narrow wrists and hips? Does it run in your family?