Hence kidney and liver function tests should be done. Other causes are diabetes and hypothyroidism.
Electrolyte imbalance too can cause nausea. IBS, gluten or lactose intolerance, parasites in gut too can be the cause. A stool test should be done for worms, giardiasis etc. Also if nothing is found then food challenge test to detect food intolerance should be done.If you have missed periods, it could be pregnancy. PCOD too should be looked into.