85% of lowest healthy weight (meaning 15% less than what you would weigh with a18.5 bmi or 17.5 if you're Asian) is the generally accepted weight for diagnosis of anorexia nervosa. In the dsm 5 osfed, formally known as ednos, atypical anorexia nervosa is classified as having restrictive behaviors and features without meeting the low weight criteria. Someone who is underweight (but not 85% of healthy weight) can be diagnosed with anorexia nervosa but it's not as common.  Without knowing more about your health and habits I cannot say as to whether you have an ed, but I'm also not a doctor and that's who you should really be talking to if you're concerned.