Duodenal Switch
First off don't panic there is nothing wrong. There could be a whole host of reasons why you aren't yet losing but it will come. Give it some time. You are still recovering from major surgery - it doesn't just magically go away but it will start to go away.
I guess the first question I have, because it messed me up at the beginning, when was the weigh in that you are comparing yourself against? Before or after the operation? I went through the operation and gained weight because of all the fluids from the operation so it took me a while before I was even back to my last pre-op weight.
Breate and work on getting in your liquids - that is the most important thing 1 week out.
Pete