Why not go back to basics?
I would suggest you make an appointment with your NUT to talk about strategies for reaching your goals.
In the meantime:
Track, weigh and measure your food.
Drink at least 64 oz of Water a day.
Make sure you reach your protein target every day.
Avoid starches, added sugars, and fried foods.
Take your vitamins and supplements as directed.
Exercise.
You have been successful before and it sounds like you know what to do. I don't see how going on a "diet" would be more beneficial than actually following your post-op program more diligently.
Best of luck and keep us posted on how you are doing.