I agree with Satay Sue
The human body naturally adapts to different circumstances.
The first time you run 10km (for example) you may burn 500 calories. The next few times your body will adapt itself to long distance running and burn progressively less calories.
Plateaus are common situations in weight loss. The important thing is, if you want to be healthy, it's important to maintain the diet/exercise lifestyle long term. Try surprising your muscles with different types of exercises: weight training, sports, cardio classes, isometric exercises, whatever you haven't done in awhile. It also wouldn't hurt to learn new exercises your body isn't used to from trainers or other gym goers.
Whereabouts do you workout? I've recently started trying to cut weight as well. A month and a half in and I've managed to cut 11 lbs so far. I'm also starting to experience a plateau.