post op 3 weeks - is vomiting now normal?
Everyone progresses to different stages at different points. Sounds like you're not ready for tuna. Might have to do softer foods for a while longer. Cottege cheese, Greek yogurt etc. and yes that feeling right behind the breastbone is where mine would hurt when something got stuck as well. That's why you're vomiting it up, because it got stuck. Try not to worry. But go back to softer foods for a week then try again.
I'm three weeks out too and have been eating tuna for about a week. However, it's tuna packed in water, and I don't drain all the water. I use one teaspoon of mayo per can (don't really like mayo) and then I split it up into one ounce servings, stirring up very well and shredding everything as much as I can. It takes me half an hour to eat that much with a baby spoon. I do it like this because I'm scared of throwing up. I have to really really chew each bite; it practically dissolves. I hope some of that helps. All that being said, I'd definitely go back to softer stuff for a few days before I'd try again. Or maybe tuna just isn't for you and you'll have greater success with other stuff :)