You can almost be as active as you want, but if you are eating too sugary or fattening of foods, you won't lose weight. I suggest you look at what you're eating, and when and why. You might be eating because you're bored, or thirsty. Try drinking more water, eating only as certain times everyday. Make sure you're eating about 1500 calories a day. Don't go under 1,000. Your metabolism will slow down, and that's not what you want. Eat more fruits and vegetables.