Why Can't U Lose Weight?
When I stop losing weight or it slows down.. I increase the fat to card ratio in my diet and also decrease a little of the protein. Here is a quote from Dr. Atkins book which has always helped me

"Since all carbohydrates and some protein convert to energy by way of glucose, eliminating almost everything but fat from the diet forces even the most resistant body into lipolysis"

If that is not the reason, you might wanna check this

http://atkinscenter.com/Archive/2001/12/26-51503.html

Good Luck.