One Week out- Not losing?

I am 5 days out from lapband surgery. I have been on liquids since last Thursday. I am keeping a food diary and I am not eating more than 500-600 calories a day.(mostly protein powder) I am not losing weight. Do you think we retain fluids after surgery? or Is there another explaination? I am still hungry and have had very little nausea. Thanks to all of you who have been down this road and can share with others.