You have already reached a HUGE milestone. You REALIZE you need help. You would be surprised how many people deny it. Talk to: Parents, school nurse, your Dr. anyone for help. Just keep talking. You will find help. Just keep talking. Good Luck ;-)
There are many useful suggestion in the replies you have received. To help yourself by UNDERSTANDING what is wrong and how to handle it, read any of these books from Amazon.com
“Confessions of a Failed Anorexic” by Michelle Cantrell; “Thinspo” by Amy Ellis; “Thin” by Grace Bowman; “The Anorexia Workbook: How to Accept Yourself, Heal Your Suffering, and Reclaim Your Life (New Harbinger Self-Help Workbook)” by Michelle Heffner, Georg H. Eifert and Steven C. Hayes; “Brave Girl Eating: A Family's Struggle with Anorexia” by Harriet Brown; “Wasted: A Memoir of Anorexia and Bulimia (P.S.)” by Marya Hornbacher.