What Causes IBS Along With Dry Heaves And Abdominal Pain?

My son is sucrose and lactose intolerant, has IBS, throws up and dry heaves daily, has arthritis, and feels AWFUL most of the time. He s on medicare disability. He tries to follow a FOD MAP diet, but most of the food that says is ok to eat, still makes him sick and his stomach hurts most of the time. He s 44 now. He was diagnosed with this about 3 years ago. His gastro dr. is not helpful, no one really seems to know (or care) how to fix this. Do any of you know how to help him? This is not inherited, he was not born with it. It showed up in his 30 s.