IBS can actually be a parasite
I was diagnosed with IBS by a GI specialist. I had noticed some other symptoms that suggested to me after much reading that I could have a parasite causing the IBS. Once the GI gave me the IBS label it was hard to get them to dig deeper. So I insisted on a trial of Flagyl as an empiric method of checking for parasites. Flagyl isn't the best overall anti-parasitic but it can effect many of the Protozoa class. So I did 10 days of Flagyl and almost all my symptoms went away after about the 7th of a 10 day course. I followed that with some stool testing and another round of Flagyl. Then 30 days on Alinia after testing found Blastocystis Hominis. All my IBS symptoms and more are resolved but testing suggests I may not have fully killed the BH so it might come back.
The moral of the story is don't let them tell you that you have IBS without digging deeper. One area that should always be checked is for parasites. Make sure they run 3-5 stool tests plus I'd try a 10 day round of Flagyl just as an empiric check.