Been there, done that. One doesn't need to be a teenage girl to "get it." So, Delia, it's time for some tough love!
You are not perfect. That's a good start.
You will never be perfect. That's a rule to live by.
Your quest for perfection is delusional. Let it go.
Sylvia Plath said women looked in the mirror as a way to remind themselves that they still existed. That is your problem. If you are not perfect, you cannot exist to others.
People with eating disorders do not lose weight easily. That is an absurd statement! An enormous amount of energy, secret tricks (which is unfair to those who love you), and willpower is necessary. People with eating disorders tend to be rather miserable and isolated. Is that what you want? To be thin (or in your head, perfect) and miserable and isolated? Your diet should consist of good foods, especially clean raw fruits, vegetables, nuts and seeds of all kinds. You should have a decent exercise program, either at school or by jogging or dancing. Tennis, anyone? How about a fun dance class, huh? This way, you are prepped for the rest of your life, the way you are prepping for college or adulthood.
My goodness, girl, you are 15 years old! Your hormones are messing with your mind! Do not forget that! This obsession will pass, but that is not an excuse to wallow in it. Listen to the other posters here, too. Cover the mirrors if you have to -- and no looking at your reflection in store windows. Quit looking at yourself so much. Get over yourself! You will have lovely days where everything is fine (actually, those days come when you relax and let it go). You will have pimples, dry skin, messed up hair, clothes that didn't quite go with the occasion, clothes that don't fit right (unless you are rich enough to have everything tailored), you will say and do dumb things, and you will be hurt by others for reasons that have nothing to do with you at all... That is part of the strange glory of life. You are alive when so many others never made it...
You are self-centered. Delia, this is partly justified as you head toward the rest of your life, but the level you've taken it is unnecessary and morally obnoxious. Get out of yourself. Consider the wars and famine in the world, the sickness out there. This will help you to put your own self in perspective. How does looking "just right" help the world? How does worrying about trivial things help the world?
I suggesst you check out the wikipedia web site and learn about the philosphy subject. There are many philosophers from centuries who will inspire you to think in new ways.
You need to start helping others, whether it's volunteering at a safe place once a week - every week, not just when you feel like it, or by visiting a senior citizens home or animal shelter. How about organizing a food drive for the holidays? You can do it through your school or set up a big cardboard barrel at your local market (with permission).
Your focus should be on being a part of the world, not on your looks and perfection. Do you keep a diary? Write about your feelings and jot down all the things you are thankful for. Make it a good, strong habit.
Again, Delia, your hormones and peer pressure (two things that are going to settle down over time) are influencing your worries. I should focus more on other worries: your family's happiness and strength in love, how you can make the world a better place with your heart, what it take for you to feel complete? You are loved and accepted for YOU, not for your looks or body size.
And if someone tells you otherwise, he or she is a fool.
Concentrate on positive thoughts. If you say, "I look awful today," change that to saying, "I am fabulous today! I am great! I can do anything and I am going to help the world with my positive attitude!"
As the years pass and you learn so much more about life and love and the glories of nature and science and God, this will all seem ridiculous. Get a head start on this now! Go find a butterfly or a bird and concentrate on it. Draw a picture of yourself with a great big smile and sparkles in your eyes, because it's all there already!