What Causes Persistent Abdominal Pain And Nausea?

My teenage girl has been suffering with severe abdominal pain, discomfort & nausea for 6 months now. She has had colonoscopy, gastroscopy, abdominal ultrasound, blood tests, stool sample tests. She has tried 7 different medications & is presently on Dipentum & Losec which make no difference. She has tried the lactose -free diet & the gluten-free diet. Nothing!!!!! Any ideas????