Hi Misseltoe, diet and weight loss plateaus happen to everyone eventually, regardless of their level of physical fitness. In fact, as you get leaner, they actually tend to occurr more frequently.

The first thing you need to do is understand whether you are plateauing because of a metabolic adaptation or because something in your diet or exercise routine has changed over time. Once you determine the cause of the plateau, then you can treat it with a number of different tactics.

For a detailed article on diagnosing a weight loss plateau and then "breaking through it" check out the following article: Weight Loss Plateau: Diagnosing and Overcoming a Weight Loss Plateau.

Best of luck and keep me posted on your progress.

Matt