Would a diet of water with an occasional Lipton flavor packer thing.....?

Help me lose 49 pounds. I'm a 13 year old boy. Bulemia isn't helping, even after years. Makes my nails brittle, and my hair fall out if I throw up too much. And my stomach hurts alot and i throw up easier. I'm 134 pounds. but i want to get down to 85 pounds. Then maybe ill work my way back to gaining it in a healthy way. How do i do it? Exercise can't seem to help after so many years of greese build up. WEll I throw up if I eat most foods. So 99% of my food intake is cereal because my stomach can take unlimited amounts of only that food. UGh, I need help