Sounds like you need to visit with a doc about all the over the counter stuff. Sometimes the fillers and additives in those mess me up.
I had my gallbladder out and now I can eat so many foods I could not eat before. I could not drink OJ, I would still be burping it up 2 days later. Now I can drink it and it stays down.
I find that if I eat artificial additives in the foods then I have trouble digesting them. I cannot eat Gar Gum, fake fat, they put in foods to make them low fat. It comes out like a slimy snake, sorry TMI....
Artificial sweeteners are super bad for our bodies no matter what the media tells you. People are having side effects from them that are almost universal and the companies are not letting anyone know since they would go out of business. So keep drinking the water but stop the diet drinks and any other diet foods with additives like that in them.
I also have IBS with chronic diarrhea. I have to watch each and every thing I put in my mouth or stay at home and plan on eating way before I put any liquids in my body.
Eating 1/4-1/2 cup of 100% bran cereal for breakfast every day is supposed to be the fix all for both kinds of IBS. Either the excess fiber will make the constipation softer and easier to expel or it will cause the excess fluids in the bowels to be absorbed and make less loose/runny stools.
Sometimes the whole foods and extra veggies will make the excess gas and bloating worse too. I would think visiting with a dietitian about what diet you body can work the best with might be a really good choice. Each of them have their own ideals too so if one doesn't mesh with you and your lifestyle find a different one.