When I was a teen, I was obsessed with running and keeping fit. I was 6' tall and weighed about 130, 40 - 50lbs less than I should have for my body size and frame.
I never considered myself anorexic because I would eat and eat and eat, even though I would run a total of about 10-20 miles a day and constantly work out. Then one day, I fell and dislocated both my knees which ended my love affair with exercise and probably saved my life. It wasn't until later in life that I realized I was going to kill myself if I had kept that up.
What I DO know from my experience is you need to find a happy balance between what you think is eating healthy and staying in shape and just letting yourself go to the point where you're sitting on the couch, eating bon bons all day and watching TV ... you'll have plenty time to do that when you're my age.
Try this website
http://www.anad.org/site/anadweb/ for help. It's the National Association of Anorexia Nervosa and Associated Disorders. All services are free of charge and they offer a toll-free help line, online support, assist in finding a doctor and more. They might even be able to help you tell your parents about what you're going through.
I wish you the best of luck. Being a teen really stinks sometimes and you're heading into the hardest time of your life - high school - you'll be able to handle it a lot better if you have your eating diorder under control. Just remember that you are worth the attention, the work and the acceptance of help when you need it.