Hello there,
I don't know you, so can only go by what you have posted. The things you mention, such as wanting to lose weight, sometimes envying anorexic girls, thinking about food all the time, and disliking your body, all point to a psychological disorder.
This doesn't mean you are crazy or it's a mental illness at all. It just means that your issue is not really food or weight, but your state of mind.
We all know the eating disorders of anorexia and bulimia. To a lesser extent, compulsive eating is becoming known too. But there is another one, obsession.
It's easy for most people to go years, and even a lifetime, without knowing they are obsessed. So many of us are dieting, or weight and diet conscious, right? But when you find that you've spent a high proportion of your day thinking about food, eating, cooking, digesting it, your next meal, calories, carbs, portions, and so on. As well as thinking about your weight, how you look in the mirror, the flab you can grab, how clothes fit, etc, then you are embroiled in obsessive behaviour.
Just like the other eating disorders, it takes hard work and time to work your way through your issues. I know it's boring and takes effort, but there are only two ways of moving forward. Either you see a therapist or you self-analyse. Unless you are academic and spiritually/emotionally mature, then the latter is not a common option.
Many clinics offer free therapy or at least support. At the very least you might find a support group. If you want to start online first, you can do that too.
These might help:
UK -
beat : Welcome to beat
USA -
http://www.edap.org
I know that advice on exercise and weight control seems easier and more immediate, but losing weight won't make you happy, simply because that is not the true underlying issue.
However, one small advice that does involve food, is to manage carbs. Simply because having your blood sugar peak and crash is only making your emotional/psychological issue harder to cope with. Stay away from or limit your starchy, white flour, and sugary foods (white bread, white rice, large potatoes, pasta, sweet foods including bananas). Eat plenty of protein to fill you up. And don't be afraid of fats such as cream and olive oil. This at least might help with cravings.
I wish you all the best.
Health and happiness come before thinness.