I don't know if you have ever had "the talk" after your surgery about food. In my case I did not and was on my own for a few years. The first thing to go was coffee, or rather caffein. Getting used to decaf wasn't too difficult. What I found helpful was to keep a journal. I recorded everything that went into my mouth and the time of day. even chewing gum. I also recorded the time and consistency of every bm. It wasn't too long that some things began to change my bowel habits. One of the first things to go was dietary supplements, like fish oil and vitamin D. Eventually it came down to animal fats. Things like, whole milk, that includes ice cream, yogurt and butter. It also included bacon, and anything fried, even potato chips. The second thing was chocolate, in any form (it could have been the caffien.) I found that chocolate sometime shows up in things that you might not expect, like some cookies that listed cocoa but not chocolate in the ingredients. The last thing, so far, was oatmeal and I think some cold oat cereal.
The thing is that some foods affect me in different ways. Whole milk products seem to take effect within two hours. Others not until the next day. Things like chocolate, did both. Sometimes within two hours and sometime the next day. Oatmeal, the next day.
At first, I tried eliminating things one at a time but that didn't work and was sometimes confusing. It wasn't until I started eliminating whole groups of things that I began to notice the difference. If it were possible, becoming vegan and adding things one at a time might have been more scientific but I was not in a position to do that.
I know what you are going through and it's rough, but you need to hang in there and find out what foods your body is reacting to.
I just might try Metamucil when I want to have some ice cream.