Hilary's advice is excellent.

We all have our eating habits, and portion size and how fast we eat are important components. When we switch to low carb, we generally wind up eating less or less often, because we are satisfied longer between meals. This results in a decrease in our daily caloric intake. Once we reach a long-term plateau, it may just be that we are now ingesting a caloric intake that is maintaining our current body weight.

At this point, since there is less of us to feed, we can work on lowering intake somewhat to get things going in the right direction again. Slowing down our eating habits helps, as does starting to use portion control in addition to the feeling of satiation, as our signal to end a meal. This is not as difficult as if we were just doing calorie restriction from the beginning, because we are smaller now and need less food, and we are more conscious of what we eat. We've also had success, and that is great motivation to keep the ball rolling.

This is my theory at least. I'm working on portion control now. I still eat like a buzz saw, finish before anyone unless its ice cream. My lovely wife beats me on that stuff every time, and I can't explain it.