hi there Anorexia nervosa is an eating disorder characterized by immoderate food restriction, inappropriate eating habits or obsession with having a thin figure, and an irrational fear of weight gain, as well as a distorted body self-perception. however in your case the main problem is Loss of appetite. the various causes of loss of appetite in your case may be due to Stress, Anorexia Nervosa, infection like mononucleosis with features like sore throat, swollen lymph nodes, weakness and abdominal pain, taking of drugs like psychostimulants, anxiety / Depression, hypothyroidism etc. A person with anorexia undergoes self-starvation or other methods to lose weight in obese or overweight girls. the loss of menstruation is a one feature of anorexia nervosa. in my opinion you needs complete check up as loss of appetite can lead to lot many future complications like low bone mass, electrolyte imbalance etc . i think you need medical appointment to rule out causes of loss of appetite esp anorexia. other wise light exercise might help to improve appetite, and relieve the stress by meditation and interaction with other people around. but personally speaking you must get appointment with your family physician for proper checkup TC