So I’m not sure if this is helpful but I had very similar issues in late middle school/early high school that was written off by both my parents and by doctors as an eating disorder (which it wasn’t!). I felt yucky every day and nauseous all the time and developed a lot of anxiety around feeling like I was going to throw up. It wasn’t super popular back then but it turned out that I had undiagnosed celiac disease (gluten). I was eating gluten every day so keeping a food journal never worked since it was such a staple in my diet. Additionally, when they were testing me, all of the tests came back pretty inconclusive so after maybe 2 years of ignoring it and a bunch of testing, Drs suggested I just try cutting it out (again, this was 2006 – wayyy before the gluten free fad started) so I did. It took about 3 weeks after that but I started to feel sooo much better, gained a lot of energy and just all around was healthier. There is a simple blood test that they can run to screen for it so maybe one place to start?
Totally different but somewhat feels the same – maybe have them test for h pylori too! another pretty easy test but in my experience, feels super similar to what you’re describing and also what I was feeling pre- celiac diagnosis.