Poor Mya. It must make her as miserable as it makes you.
We went through some proper poorly tummy issues with Sam when he was younger. In the end to work out if it was food related, and what food it was we starved him for 24 hours, nothing but water. ( You can imagine how happy our little trencherman was lol) . Then we introduced one food at a time . We started with plain boiled rice, after 24 hours we added plain chicken , after 24 hours we added scrambled egg . After that it was the addition of one food every 24-48 hours.
Sam needed a grain free diet as it turns out. We also added veggies for fibre and roughage to his diet every few days .
I think its going to be slow going while you work out which food is causing the irritation but I think it might be the best way forward.
Good luck with it and feel better soon Mya.