How To Gain Weight Quickly With a Fast Metabolism?

I was the same way you were when I was your age. I am now 22 and am a normal weight. You don't need to worry about trying to gain weight. It will come eventually and you will regret worrying about it at your age. When I went to the doctors for it they gave me protein milkshake drink powder packages which will help you gain weight. I hope you are not trying to not move around much so that you don't lose weight. Your health is more important than that. With moving around more you will actually probably gain more muscle which means you will gain weight because muscle weighs more than fat. If you move around more your appetite will also probably increase.