My IBS, though, tends towards the other direction, so fiber is absolutely essential for my own IBS. I use
flaxseed meal, rather than psyllium, because it is gentler on the whole system. Psyllium irritates my GERD for one thing. I don't have this issue with flaxseed meal.
But, I don't think this is the entire issue at hand for you, so I would strongly urge you to see a GI as soon as possible if you haven't already done so.