I've had a formal diagnosis of IBS (D-type) for over 10 years now. These days it's a bit better than it used to be, but it still plagues me at least four or five days a week and seriously impacted my ability to work when it was most active (I'm on a Disability Pension now, though not specifically for the IBS, that's a massive part of it).
Mine is both diet and stress triggered. If I'm not stressed, I can mostly manage it with my diet. If I am stressed, it doesn't matter what
I eat, I'm going to be miserable and in a lot of pain. Unfortunately, things that stress me include seeing friends / going out to dinner / going to doctor's appointments etc. My way of dealing with socialising is just to not eat for about 12-8 hours beforehand, not very practical, but thankfully I'm not a socialite. However, this has done a number on my metabolism, since I've had to semi-starve myself on and off for ten years. Ah well!
I am still grateful that...with time, and as I improve my stress levels, it does seem to be improving. It's not something that will go away overnight, but any improvement is a good one!