You are eating to little. Your body will go into a starvation mode. It will store all of the calories you take in BUT, it will burn them. When you eat nothing your body takes calories from your fat, your muscles, and if you let is go on long enough (in the case of anorexics) your organs. If you eat only 500 calories a day you will loose weight. That is very few calories though, and will decrease your health and energy levels (eventually).
PLEASE GET HELP :-/