One thing I picked up today that I thought might be useful to you. The nutrition chap said to ensure we are fuelled all the time, which I know you know. But he also said that when you work hard and fast you burn the glycogen but if you work at a steadier pace for longer, your body learns to burn fat. I wondered if you were working too hard and burning your glycogen rather than fat which is why your weight isn't going down?
Ideally you need to be burning glycogen and fat.
Hope that makes sense!