"Only" nausea? Any burping, heartburn, stomach burning, changed bowel habits or stool color? Faintness, pale skin, tingling or numb arms?
When (after eating, at night...) and where (upper middle stomach, lower stomach...) stomach pains appear?
Common deficiences in vegetarians are:
- iron deficiency
- vitamin B12 deficiency
- hypoglycemia (low blood sugar)
I'd recommend blood test for iron, vitamin B (vit B1, B6, B12), glucose and main minerals: K, Ca, Na, P, Mg.