I'm not a medico but my own experience leads me to suggest that you make sure the diagnosis is right, and that the situation has been properly investigated.
I used to have what was called IBS. It was debilitating. It did seem to get worse with stress. Ingesting fat certainly caused problems.
It wasn't IBS. An abdominal ultrasound finally identified gallstones; masses of them. I had the gallbladder out and whammo, suddenly no more "IBS".
Make sure the diagnosis is right, as the symptoms cross over with other conditions.
Good luck!