Sometimes you can hit a "plateau" when you're trying to lose weight. Here are tips from Duke University on how to cope with a plateau:
Don't weigh yourself more than once a week. More frequent weighing may record normal weight fluctuations, making you think you've stopped losing.
Keep in mind that everyone is different. Your rate of loss is likely to be different from the next person's rate. The more you lose, the faster the pounds will drop.
Keep your exercise workout at a moderate level. If you exercise too much, your body may start hoarding calories and fat.