Eating disorders are medical conditions that can be diagnosed by doctors who can and do prescribe treatments for such conditions depending of course upon the severity of your symptoms and conditions. You need to meet with your school counsel and administrators as soon as possible, hopefully with a parent or advocate. You will need to provide documentation of your medical condition and request appropriate accommodations under Section 504 of the federal Rehabilitation Act. As eating disorders have both physical and emotional components, you are entitled to request appropriate accommodations.
Good luck with getting the school to acknowledge your special needs.
This advice is not a substitute for a thorough evaluation of all of the facts of your case by an attorney or advocate with a background in education law for children with special educational needs.
The impact of sharing your illness with your school depends on whether it fits the legal definition of a disability. Under the Americans with Disabilities Act (ADA) and § 504 of the Rehabilitation Act of 1973 (§ 504), a disability is a physical or mental impairment that substantially impairs a major life activity, a record of such impairment, or being regarded as having such an impairment. Major life activity includes eating and the function of the digestive system. If your illness is not a legal disability, then sharing information about it with the school is not likely to make an impact. If your illness is a disability, then sharing it with the school will likely trigger some helpful protections.
Generally, institutions that receive federal funding, which include most public and private schools, cannot discriminate against any individual on the basis of disability. Under § 504, non-discrimination includes providing reasonable accommodations to enable individuals to participate in the activities provided by the institution. To get accommodations in a post-secondary school, the individual first needs to disclose their disability to the Office of Disability Services, or equivalent office, at the school with documentation showing both the disability and its impact on education. The school then must provide reasonable accommodation(s) to address the disability. The individual is encouraged to propose accommodations, but the ultimate decision about what accommodation to provide is made by the school and is only required to provide access, not provide the optimal situation for the student.
If you want to pursue this matter further, an education lawyer licensed in New York would likely be able to help you. The New York Department of Education provides information about Parent Training and Information Centers for New York that provide disability and education related resource to families at http://www.p12.nysed.gov/specialed/techassist/parentcenters.htm. The Commission on Quality of Care and Advocacy for Persons with Disabilities is a federally mandated protection and advocacy agency that provides legal services for individuals with disabilities in a wide variety of settings, including education and can be found at http://cqc.ny.gov/advocacy/protection-advocacy-programs. The Council of Parent Attorneys and Advocates, a special education advocacy group, provides a directory of attorneys and advocates at http://www.copaa.org/find-a-resource/find-an-attorney/. The New York State Bar Association also provides information about lawyer referral services to help you find an attorney at http://www.nysba.org/AM/Template.cfm?Section=Public_Resources&ContentID=67283&template=/CM/ContentDisplay.cfm.
This answer is given for informational purposes only and is NOT legal advice. This answer does not establish a lawyer-client relationship. If you need legal advice and assistance you should contact an attorney in your local area immediately.