Picky, picky sleeve!

I found great-tasting Basil Pesto tilapia fillets at costco, 18 gms of Protein and 120 calories for a 3 oz. serving. I have been having them for about two weeks now, the box is about half-gone. Never a problem eating them, they make their own sauce when you microwave them and the fish is flaky and moist. I made one for lunch, ate it watching the noon news, and I have had a stomachache ever since! I did not eat too fast or too much, it's just that today my sleeve decided that it didn't want tilapia for lunch. I can feel where it is (or was), in the bend before the duodenum, because that's where it aches. Thankfully, it's getting better as the day goes on, but honestly, I would like my tummy to settle into some predictable behaviors--no bread, okay, I can live with that. But tilapia is okay for ten days but not the eleventh? Beef tips are okay on Sunday but not on Tuesday?

Has your stomach settled down and become predictable?