i'm sorry you're going through so much pain at such a young age; I have all the same stuff you have minus the gallstones. acid reflux, sore throat that won't go away, scratchy and raw feeling, and i'm sure i have a stomach ulcer. haven't had it checked becuz no insurance right now. but the burning and nausea kept me up half the night. it's miserable. i'm much older than you though but do remember having some gastro problem after having my son years ago. i wonder about hormones playing a part.
anyway, i'm curious what the doctor will do about your ulcer. probably meds.
I'm sure you know this, but you have to eat very carefully. no soda, no alcohol (that's the worst), and probably nothing spicey. i eat a lot of dairy cuz that's what my body seems to crave and i have an appetite for.
i hope you can find some relief from all this soon and good luck with your GB surgery. I hope that helps some of the symptoms. take care now.