I also have a tiny Dr. Anthone tummy. Today I am 4 weeks out from surgery, and I've also noticed that some days I'm MUCH hungrier than others, but I can only eat a maximum of 3 bites before I get sick, which I try to avoid but happens sometimes.
I too, before surgery was able to eat 2 fast food meals at one time. At Burger King, I would eat a full-size Whopper with cheese and bacon, a traditional chicken sandwich (the one on the hoagie bun), most of the 2 sets of fries, and most of the REGULAR Cokes that came with the meals! At other times, I could also eat a whole steak burrito with guacamole added from Chipotle, in addition to chips and guac or salsa and a REGULAR Coke! With pizza, I could easily eat 1/2 of a large 3-topping pizza (4 pieces), plus breadsticks and sometimes a salad. With a regular soda, of course. So right now, I'm eating way less than 1/4 of what I used to eat. I was always a big eater though, even as a child, although I was lucky and was not overweight while young. When I was with my ex-husband, I could out-eat him easily!