youre not fat at all. and anorexic people are actually able to gain weight pretty easily because when they starve themselves, their body goes into starvation mode and anything thats put into the body after that gets directly stored as fat. some girls that are tiny can eat what ever they want because they have high metabolisms.
now, anorexia is a mental disorder just as much as it is an eating disorder. it sounds like you have pretty good control over it. so my advice is to stop it before it becomes a serious habit and you become obsessive over it. its more dangerous than it seems. if you continue to eat less you may think you have control over it but one day you could get dizzy and pass out for a second, get freaked out and try to eat and discover that your body rejects any food you put in it and you start throwing up uncontrollably.. yeah, its dangerous and it will take control over you sooner than you think. so stop while you still can and be healthy by working out an hour a day, 6 hours a week. and eating healthy foods like fruits, veggitables, whole wheats, and lean proteins (in the right portions) and it will work..
when you think about it, being healthy really is easier than not eating.
if youre having trouble changing your ways, try incorperating one new thing each week.. such as working out for a half an hour, eating more fruits and veggitables, or eating less unhealthy food.