I don't believe you are anorexic. I have read your other posts and I believe you said your age is in the teens? Something like around 15? I think you have a high metabolism plus, you are young and you also said that you eat whatever there is. At your age, you are fine. Only a doctor can diagnose whether or not you are anoreic. But based on what I read about you, I think you have no weight problem.
I, on the other hand, am older, (30) I restrict my calories and count my calories constantly. I have a lower bmi because of the way I plan my meals.
I know I have an eating disorder. You do not sound like you have an eating disorder. I think you are healthy. My sister was really low in weight at your age too. She had the same thoughts of it being anorexia. The doctor said she was normal. She gained appropriately as she got older.
I really don't believe you have any problems. You are young, you eat, you probably have a high metabolism.
Now I am not a doctor, and I am not saying you do or don't have a problem. Again, remember that these posts are just for advice and opinions but in MY opinion, I think you are a healthy teen. If you are concerned, go for a physical from your doctor.
But like I posted earlier, check out my post about the accuracy of the bmi. The post is titled: How accurate is the BMI ? I think it is at the bottom of the first page or the top of the second. BMI is really not too accurate from what they tell me.
Either way, accurate or not, best to get checked out by a doctor. I still think you are healthy though.