What Causes Intermittent Vomiting,headaches,blurred Vision And Abdominal Pains?

I have a freind who has for a few years now had an off and on periodical illness in his abdominal. The symptoms are uncanny and fluctuate between a few hours and a few days. These symptoms include, vomiting, headaches, temporary blurred vision, abdominal pains, and a mass in the stomach that comes and goes within hours. He has seen numerious doctors whom do not know of what it may be and because the mass comes and goes some doctors dont even think the illness exists at all. is there anyone that would know what would cause this and or how it can be treated? if no one is able to find out what it is may i be given a doctor who may specialize in this or may be interested in this illness? we live in Austin texas. Please help us. Thank you.