What Tests Are Used To Diagnose Persistent Nausea, Gagging, And Upset Stomach?

For the last week, I have been suffering an unusual upset stomach, slight nausea and an increased gag reflex when drinking or eating. I'm wondering what types of tests are common for diagnosing whether or not my symptoms are symptomatic of a more serious condition. Can you advise me what to do in the meantime to treat these symptoms or their cause?