I Have A 39 Year Old Son Who Suffers From

I have a 39 year old son who suffers from severe abdominal pain. He has suffered with this since childhood from the age of 9. He usually suffers with this first thing in the mornings. He has learnt different technique over the years to help manage his pain levels, eg hot showers and breathing exercises. He has been on tremole for the past 4 years and helps most of the time but approximately every 2 years it gets totally out of his control and he continuously vomits and sweats and curls up into a fetal position and slithers in pain. When this happens we call for an ambulance where he is taken to hospital only to be released again when they get the pain under control. Usually this happens 4 or 5 days in a row , meaning we send him to hospital everyday, or take him to his GP where they send him to hospital. The latest diagnose is IBS, but I have been told vomiting is not a symptom. Any Ideas that we can explore to help.