Suggestion: I had a lot of bowel issues, including IBS for 10 years and discovered it was due to candida. Have you considered that possibility?
I began taking horopito oil and my 10-year-diarrhea went away in days! You might consider trying it; if it works, you'll know it is candida. There is also a blood test for candida if you require absolute proof before trying a supplement. Good luck.