I had exactly the same situation. I stalled for 3 weeks. It seemed impossible not to lose, but then I decided I wouldn't lose unless I exercised, so at 5 weeks I started doing a little bit and increased it over time. The first 2-3 weeks I lost 20 pounds, and then nothing. I feel like those 20 pounds made me able to do more exercise than previously. The exercise got me out of the stall and now I'm not losing fast, but I have gone down several sizes- 26 to 18- 4x to 1x. I would have quit after the stall as I always did on diets, but this time I have made a commitment so I keep going! I am now at week 15, and I have lost only 40 pounds- about 2 pounds a week after the initial loss. I am just a slow loser, as I am following the diet, and it's still slow- I think some people only eat 6-7 hundred calories a day, but I wasn't losing if I ate too little. I think I need at least 1000 calories, and all my assigned amount of protein (91 grams) to lose. Maybe if I had exercised and stuck to my diet for more than a month before surgery I probably could have lost weight, but I couldn't, so now I am! Just don't get discouraged and remember this isn't magic, it's a new way of eating, and exercise! Good luck!
