I have taken zofran for nausea and it seems to actually make me worse and vomit. I have IBS and when I have an attack I disolve a Symax FasTabs (levsin with a unique distribution to get into system fast) tablet under my tongue. The generic does not disolve. You need the brand. NuLev was best but they don’t make it anymore. I also have gastroparesis (quite significant but not with all your bad symptoms). Unfortunately for me it does not make me lose weight even though I have little appetite.
It sounds like you have much more than IBS going on and don’t let them push it off as psychiatric! I wish you could get worked up at Mayo clinic. I’m sure with the way they do work ups there they would figure this out.