Although every surgeon's post op is different one thing I think is consistent is being on those liquids the first 2 weeks. You've eaten part of a sandwich, oatmeal, etc really too much for your new stomach. As I've stated in a previous thread, compare your new stomach to a baby's stomach. At one week old you wouldn't give a baby a piece of sandwich or Cereal...you give him liquids.
Your surgery will help you loose the weight but it's a tool you will have to do your part. Get your Protein shakes in and sip your Water throughout the day. You can do this! You just need to get a regime going