Everyone is different. When I went to a support group, I met a woman who was getting the Bypass. Two weeks after her surgery, we all had another support group, and the woman who had the Bypass hadn't lost a single pound. She was doing everything correctly, and she was so confused as to why she wasn't losing weight. But a month later after that, I met up with her again, and she had lost over 40 pounds. Your body is probably in, what I like to call, "pioneer mode". Right now, your body is probably in a slight panic because it's not used to this new way of eating. It's trying to hold onto every last calorie that it can because it thinks that it's starving. You can't pull your body aside and say, "Hey look, calm down. You're allowed lose weight, because I'm just changing things. Don't worry, you're not dying." Lol.
Make sure you tell your surgeon about your concern and see what he/she thinks.