dude i think it would be seriously unhealthy for a 15year old to be 7stone, no matter how small you are. Why dont u try doing some toning exercises? do you know muscle weighs far heavier than fat?? so if your doing sit ups, push ups, squats, etc, along with cardio exercises such as running, walking etc, your are actually loosing inches but will stay roughly the same weight or not loose as much, but this is not a bad thing, muscle makes you look defined, toned and slim. dont be afraid of becoming bulky like those weightlifting women, they are freaks of nature, and belive me i know my stuff, i study the human body in university. look at the way britney used to look, she was so toned and muscular, il bet you she weighed about 8.5 to 9stone cos she was so muscular, but it was hot! so please dont try to go by the number on the scales, measure urself every week instead and i garentee ul notice changes quicker than you would by just doing cardio. good luck chick