Up to 30% patients will experience diarrhea
Surgery) and it will gradually improves with time.I too fell that both IBS and Bile acids are playing role in your diarrhea even though you haven't mentioned anything about abdominal pain
.As you are under the care of Gastroenterologist and is on right medicines I guess you will improve soon or else you may need some some dose/medication adjustments.As you might have been already explained by your Doctor,stress and anxiety
worsens IBS ,thus I suggest you not to worry too much about the problem and be as relaxed as possible and you can ask your doctor for some anxiolytics.
Wish you all the best