You are in a tough position. I am a mother of two sons - one who is 45 has had IBS, etc. for years. He is pretty open with the problem but does not trust the doctors.
If your son is seeing a gastro doctor - clinic or group - ask him about talking with a nurse practicioner or physicians assistant about medication, food, anxiety - just dealing with this disease is very hard. I am pretty new at it at 68 and still having problems talking about it with my family, etc. I have two NP's I just love. One is a young man and gastro NP is a young lady - she listens and helps me understand what is going on and what I have to do. They are more compassionate and have more time to just "deal" with the patients - medically and emotionally. Also, maybe a support group.
ElaineNY