Plateauing is definately normal! I think just about everyone who has lost weight has reached at least one at one point or another. Our bodies are amazing creations and will adapt to whatever you're doing quite quickly, which is why personal trainers generally recommend you change up your exercise routine every 6 weeks or so as your body gets used to it which can be very frustrating.
Depending on what you're doing (daily calorie intake, exercise, etc) you will probably need to change it up. If you're already on a low calorie intake then you might want to include a higher calorie day to get your body confused and increase your metabolism. Or if you've been having the same calories since the beginning it might be time to decrease them a little because the smaller you are, the less calories you need.. but make sure you're getting the right amount otherwise your body can go into starvation mode (another unhealthy plateau!). Otherwise maybe having an extra exercise day per week will be what you need. The Calorie King website has great information about diet too if you haven't already checked it out!
Hope this has been helpful, GOOD LUCK and I'm sure you will break through it!
This week's goal... control portion sizes!