Obviously everybody is totally different and what worked for me won't necessarily work for you... but this has had SUCH an impact on my life I had to share:
Getting a Brita filter and only drinking filtered water has all but fixed my digestive issues after years of pain/bloating. (Still the odd food item that sets it off but I'm 90% better than I was!)
I've had really bad IBS-D for several years, think first sip of tea in the morning had me running to the loo, can't plan any kind of social meet-up without knowing exactly how far it is to a bathroom... Lived in London for 10 years and it's got steadily worse.
I think maybe the chlorine in the London water was upsetting the balance of bacteria in my gut...
Worth a try if you are in a similar position!