I was looking into how an intestine afflicted with IBS functions, and I found two interesting and indepth articles that helped me to understand these functions:
They're a bit complicated and took me a while to understand but do give them a look if you can.
My take away from these articles is that tricyclic antidepressants may work to dull or even nullify the gas-associated pain and nausea that comes with IBS. I'm not in the right head space to explain it all in detail, apologies, but long story short, tricyclic antidepressants block certain receptors in the gut that would otherwise send neurotransmitters (such as serotonin) to the brain and set off a painful, nauseous and anxious response.
Two of these antidepressants, Nopramin and Nortryptyline have very good reviews on drugs.com. The dose needed is very small, so hopefully the side effects would be minimal for most. An option to consider if you're already tried many lifestyle changes to no avail.