Heather does give Oregano as an herbal supplement to treat IBS (sorry I said otherwise before!). I don't think the people replying to this thread, including me, knew that oregano was something Heather recommended.
However, the product on the Amazon page that you had provided a link for does not say it is enteric coated. Not all capsules are enteric coated, and it may dissolve too quickly, causing you pain.
Have you tried Heather's Peppermint Capsules? I found them more effective than some other supplements I've tried (fennel, ginger etc..).