Hello, Firstly as the other answers rightly said, go see a doctor. At the age of 16 it is uncommon but not unheard of. What you are describing is medically known as Genuine Stress Incontinence. The first thing that springs to mind is what is the root cause? Have you ever had a fall where you have hurt your back (spine), neck or head? Have you had prior surgery in the abdominal area where they needed to cut through the pelvic area? These could be contributing to the weakness. You need to understand how the body works to be able to correct some of the things that need attention. Its easy for people to say "do your pelvic floor exercises (kegal exercises) and that will put it right" But knowing how to do them correctly and continuously doing them is the key. I would suggest you see a physiotherapist or continence nurse as they are able to show you how to identify the correct  pelvic floor muscles. (you can find more information on my blog http://pelvicfloor.wordpress.com ) If you are using tampons I would suggest Incostress. It a medical device used in clinics and hospitals in the UK, Canada and several other European countries. It is made from medical grade silicone and works by supporting the urethra (the tube which allows urine out of the body from the urethra) it also supports the bladder neck and gently allows you to exercise the pelvic floor naturally. If you are not used to tampons then do not use this. Speak to your doctor and get him to see the information on www.incostress.com