Well, the average weight for your height is 8 stone 10 to 10 stone 10, i know this as i am also your height. If you eat normally, there won't be alot you can do to put weight on. Enjoy being the size you are, as long as you are fit and healthy thats the main thing!
I'm 16 too and am the same height as you. I weigh 9stone and a bit - make of that what you may. As SGKelloe32 said as long as you are healthy and are eating properly then there isn't realy much else you can do. I hoep this helps! xx