Hi,
This happened to me last summer. I exercised all the time, followed the diet to a tee and didn't lose.
I then got diagnosed with low thyroid disease and got put on medication.
I am now starting this diet again to see if I can lose the 15 lbs I gained.
Hopefully it will work.
I had no energy last few years and other problems and had thyroid blood tests done. My numbers came back in the normal range, but I found a dr. that would treat me for my symptoms not just blood test #s and feel so much better now!

Check out this site and read up on it.

http://forums.about.com/ab-thyroid

Hope this helps.
Sandra