You're not alone! Here is a link to a thread Diane (Quest) started a couple of weeks ago on the 50 Pound Stall. It references a thread I started previously on a similar topic.

http://forum.lowcarber.org/showthread.php?t=164447

I don't have the answer for why we suddenly stall out or turn into turtles. I think it is more complicated than simply the fact that our bodies are smaller and need more calories. Some of my thoughts on this are in the thread.

However, I have been experimenting with low calorie, low carb dieting and I lost three pounds last week. If you want to see what I am doing, read the last week of posts in my journal. Quest also is following a similar strategy and has some posts about it in her journal.

Good luck!