Anorexia is an eating disorder, and it doesn't exclusively mean that you're underweight I think. At your age I was about 5'3" and weighed less than 100 pounds. I graduated high school at 5'6" and weighing about 120. I don't know what you look like, but I don't think anorexia can be diagnosed by weight/height/BMI alone. Eating habits play a big role. Are you active, or lethargic? If you're extremely lethargic then you should see a doctor for that too. Metabolism, Viatmin D, Iron, and Vitamin B-12 deficiencies could cause lethargy and if you're just not expending much energy throughout the day then you'd naturally eat less food.
On the other hand, I'm not a doctor and it could be something much worse too. Lethargy is just one example of why you MAY be eating less. I have no idea, but wanted to give you some ideas that you can work with your family and doctor on exploring maybe. Good luck to you!
P.s. Are you on adderall or anything (meds for ADD)? They have certain side-effects too that can reduce appetite. Staying well-fed is important though or you'll get dizzy and weak, sickly, or worse.