Gained? How? WTF????

I started at 101. I starved For a day, weighed myself, and I weighed 102. I starved myself a second day and went to the gym to burn off 500 calories (I wanted to burn 1000 but I almost fainted). I weigh myself this morning: 103 pounds!! I am freaking out! What is wrong with me? How can that happen- is it the Prozac? It's never happened before! I'm so sad right now, I don't know what to do about this. I wish my mom still had those diet pills, I could really use them right now.