Hello. My 18 year old daughter has suffered from chronic

Hello. My 18 year old daughter has suffered from chronic nausea for a few years. It came on after a stomach flu she had, and it has never gone away. She takes pepto bismal to relieve it. She does not have gerd, nor is she pregnant. Doctors have been baffled, and never given her a diagnosis. Can she get an ultrasound or anything that can possibly find out why this will not go away?