The first thing that jumped out at me is the Slim-fast shakes. Which ones are you using? Honestly, most of the ones I've seen are way too high in carbs and low in protein to be helpful for us (if you could post the nutrition info for the one you're using, we could tell you for sure).
My go-to for protein, especially early out, was the Premier premixed shakes. They are available at Sam's and Costco and have 30 grams of protein and only 5 carbs (or something like that).
Having said that, anything thicker like a protein drink is going to take longer to get down at your stage in the game. By then it was taking me about an hour and a half to drink a 11oz protein drink. Now I can get it down in about 30 minutes.
A few other things to keep in mind:
1) which scale did you weigh on to know you lost 7 pounds? If it's not the same one you're using now, they may not weighing exactly the same, so you may have actually lost a little more.
2) Your body has just been through major surgery and needs time to heal. You're still swollen (whether you feel like you are or not... your tummy is still swollen and will be for a while).
3) Make sure you are getting in all of your liquids, especially if soup is one of your go-to foods. Soups are notoriously high in sodium, which could be making you retain fluid. The only way to fix that is to take out the soup or to drink more fluid to flush out the sodium.
One more thing... I started my "three week stall" as everyone here calls it when I was exactly two weeks out. Yours may have just come extremely early. If that's the case, it's normal, and will pass. You just need to keep moving forward and meeting your goals for the day, and the scale will eventually behave again.
Hope that helps!
Highest weight: 277 Starting Weight: 250 Surgery Weight: 241 Current Weight: 130
Goal Reached in 10.5 months :)