If you’ve lost 5lb in 9 days, then I think you should be happy with that. I know you want to lose 2 stone and I’m guessing that brings you either to a ‘healthy’ (not overweight) size, or maybe even an ideal size. Bear in mind some of the people in this study (and in this group) will have wasaay more to lose – some might drop half of what you want to lose in total in the first week in water alone… but they might have another 100lb to lose after that.
Be patient and probably modify your expectations, especially as you get closer to your target. Even on 800 calories a day, once your body approaches a healthy weight it will hold on tight to any residual body fat for as long as it can.
Good luck!