Am I doing something wrong?
Don't stress out about it. Your body is still healing, and probably retaining water. Stay the course on your liquids, try to get in protein, and the weight will come off soon.
No, you're not doing anything wrong. Some folks' bodies stall about 3 weeks out. I was more like you. You're only a week out and your body is recovering which means some swelling and some fluid retention.
I know it's hard to be patient when the scale isn't moving every day or nearly so. I can remember hitting a short stall at a couple of months and being convinced (utterly convinced, mind you) that I had done all this for nothing and was going to be the first person in the history of the world to maintain 262 lbs on under 800 calories a day. So I know how you're feeling right now. But guess what: I wasn't and you won't be.
Some folks also lose in clumps: nothing, nothing, 7 pounds, nothing, 5 pounds, nothing, nothing, 10 pounds and so on. If those folks stay on plan, they average the same loss over time as folks who lose steadily but can get a lot more frustrated until they learn their pattern.
My suggestion is to stay off the scale until you're one month out except at any follow-up visits. Focus on healing and mastering your new eating plan. You can't control the scale, but you can control your plan and your exercise once allowed. If you do those things, the scale will follow along - just maybe not as linear a loss as you might have expected.
Highest weight: 335 lbs, BMI 50.9
Pre-op weight: 319 lbs, BMI 48.5
Current range: 140-144, BMI 21.3 - 22
175+ lbs lost, maintaining since February 2012
Thank you for this question, and thanks to everyone who answered. I've lost 12 pounds since surgery day, but have stalled for a couple of days now. I'm going to be like you and just leave that scale alone for a while.