I'm IBS-D, but I am extremely sensitive to oatmeal. So much so that I really can't tolerate very much at all. I would try eliminating it altogether and then seeing if there's a difference. Remember, people are sensitive to different things - this might be something that particularly irritates your tum. Oat meal and brown rice are in the insoluble fibre class, but are considered the most gentle (partly soluble). It could be that you're just not tolerating them well. Try some other things and see if there's a dif.
-------------------- Formerly HanSolo. IBS, OCD, Bipolar, PTSD times 3.