you got a eating disorder, there are many specialists on this subject that can help you out. it might also be due to anxienty. either way you need to see a doctor becuase it cant be healthy to be weighing that and not getting the proper nutrition. do you throw up alot? try taking a daily vitamin to get all your essentials your body needs like calcium and iron and shit like that. the vitamins aint going to make you weigh more just make you healthier overall.