I don't claim to be a IBS know it all but I've read in many a place that it is thought that IBS is just a yeast infection with a medical name - meaning they are the same thing. Yup, oil of oregano is likely to put anyone through some discomfort if they have a yeast issue of the gut (I'm the queen of Fungus) but it is a good thing to get rid of it and it usually only last a few days and almost never longer than a week.
Perhaps you all could try 1/2 of what is recommended as the dose so your die-off effect won't be so strong.
HTH
Jeannie