If you haven't tried it already, you may want to look into the FODMAP diet. Each letter in the word "FODMAP" stands for a type of carbohydrate. I worked with a dietitian but there are a lot of books and online sites that will explain the diet in detail. For the first 6 weeks it will be an elimination diet, including wheat and dairy. After that you will add each type of FODMAP to help determine if any of them are causing problems. I've been following it more or less since the beginning of 2018 and have been doing much better. I found that high fructose corn syrup in most regular sodas, and all breads except sour dough (which is allowed on the diet) are problems for me. The cause of IBS can be different for each of us, but it might be worth a try!