So I had nausea for months with no explicit cause. Saw a few doctors, had even a full gastro inspection. My naturalpath then put me on two things and it cleared me up. Both of these are over the counter natural supplements. Might be worth trying...

Pepzin GI (Zinc-L-Carnosine)- 1 capsule 2x per day 75mg Quercetin- 1 cap 2x per day

If you decide to try this make sure you go with good supplier. E.g. thorne or pure encapsulations