I've been doing quite well for a long time - no major flare ups - ticking along on low fodmap, prebiotic fibre, pro-biotics and no sugar, wheat or dairy. Then I started experimenting with adding some things and I think it kind of built up as I had the mother of all flare-ups after trying lentils which were also a bit too spicy.
The pain was awful and went straight to my mid back so I was walking like Quasimodo as I couldn't straighten up. Long story short - usual total lack of help and mis-diagnosis from conventional medicine. I was recommended two excellent acupuncturists at our local clinic. Traditional Chinese Medicine has been around for about 3000 years so I thought they might possibly know a few things and I'd seen it recommended on here.
I am posting in case this is helpful to somebody else. The back pain was because there is a major junction in the middle of the spine where the inflamed large colon meets a bundle of nerves in/near the spine and presses on them. It is almost always what they call the Spleen Meridian involved with IBS both C and D and if you can't face the needles (they are so fine it is almost painless) you can also help yourself with other things.
Probiotics and Pre-biotics were recommended and a good quality organic turmeric supplement in capsule form or added to food. No cold food - lots of stir fries, root vegetables, small portions of fish, meat, eggs etc - mindful eating with lots of chewing to help digestion (there are no teeth further down the system).
I'm walking upright again and have some energy for the first time in months. I hardly dare even whisper this but I'm already seeing a difference in the bathroom. I was already pretty clear of dairy, wheat and sugar so I responded quite quickly. It might take a lot longer if you are having those things, but it's extremely comforting eating warm food. Well mushed up warm root veg soup - equal quantities of potato, carrot and white cabbage with the green tops off two spring onions and a teaspoon of tarragon with a little chicken stock - is about the best thing I have ever found to help a flare up.