Lisa has asked all of the right questions.
I would say first that you should figure out what your caloric intake and expenditures (approximately, anyway) are. Then you will need to look more closely at your diet. You might find that you're eating more calories than you thought you were or that you aren't burning as much as you thought. Both of those things can lead to stalled fat loss.
If you haven't checked it out, you might take a look at
Leigh's books. A lot of the information can be found here, too, so wander around the forums and read what's already been asked and answered. Most of the time, it comes down to 1-you're eating more than you think and 2-you aren't burning as much as you thought. Hormonal fluctuations can influence things, but look for simpler problems first.
