Is IBS sequence really understood?

Hello, I've had the IBS and Lactose issue for 40 years but only now trying medication to eat some fun stuff. I have the bloating and unable to burp and then the Diarrhea like prepping for a colonoscopy but with severe cramps instead. I've never been able to figure out what food caused it. Tried taking Dicyclomine for several month and twice when I tried to eat something fun, even with Lactaid, or maybe it was that half a cup of coffee I hadn't had for months, I had bad nights. Probably a little cole slaw.... No more Dicyclomine. The question is, does medical science know for sure how long it takes before the offending food causes a meltdown in our large intestine? Was the problem food consumed in the last 24 hours? Could it have been 24 hours or 48 or longer and it can take that much time to cause havoc? If physics of the bowel is that it must have been within 24 hours, it would be a lot easier to figure it out. Also, has anyone found a IBS drug that is worth taking to eat a a slice of pizza now and then? Thanks and have a great weekend.