My mum thinks i am developing anorexia nervosa...someone please help?

Don't focus on losing weight so much. Focus on being HEALTHY. That means eating correct diet, getting enough rest, and exercising. Please go to www.livestrong.com there is a lot of tips on healthy living in there. If you practice healthy living, your weight will adjust to your ideal weight automatically. You are still in growing period, it is VERY important that you eat nutritious food, and enough exercise and rest. The choice that you make now, can have a very important effect throughout your whole life. Good luck.