Why didn't I lose any weight?

Sounds to me like you didn't eat very much. If you don't get enough calories your body actually goes into starvation mode which in turn makes you gain weight instead of losing it. The reason that happens is because your body recognizes that you haven't gotten enough calories and stores the calories you do get in order to prevent you from dying from starvation. Just be sure to eat at least 1200 calories a day if you don't exercise. Unhealthy eating, no matter how little you eat is still unhealthy. Try replacing some of the unhealthy choices with things such as low fat ice cream, carrots, and fruits.