I have the exact experience as yours... I went to my first post-op appointment (10 days post-op) with 13 lbs down. 3 weeks later i'm still only 15 lbs down. Buuuuut, I've noticed a change in my body, I can see that my neck and shoulders look slimmer, my upper belly has gotten smaller, so have my thighs.
So, don't worry about the weight, just keep focused on your protein and water intake and really do make an effort and get some walking into your day, it made all the difference for me.
Good luck!