I was diagnosed with IBS at around the age of 20. I then had stomach problems for the next 40 odd years or so, moving on eventually in my late 40s to upper gut issues with gastritis.
I was not diagnosed with ME/CFS until I was in my late 50s, and by then I had begun to sort out my chronic gut problems by changing my diet drastically, (at one time, no grains, no sugar, basically Paleo), introducing digestive enzymes, kefir, a variety of digestive supplements, and eventually seeing a medical herbalist.
In the past year I have been able to reintroduce fruit, and some grains (not gluten), and at long last my stomach functions the majority of the time without pain, diarrhoea or constipation. I still have ME, though it's not severe, but I am very limited in energy and have to pace. I also have immune problems though the herbalist has improved things for me.