Christine, I've tried so many kinds of fiber... psyllium capsules, psyllium powder, psyllium seed powder, citracel, metamucil, etc etc. The only one I think that works for me are the metamucil wafers. Maybe because they are in such a different form of fiber, they might work for you, too. I don't like the calories they have or the wheat, or any of the other additives, but they really are the only thing that have worked.
I don't know if you want to use them during the flare and you said you can't tolerate fiber, but maybe when the pred kicks in, they might help, even having half a package.
I'm sorry to hear about the flare and sending good thoughts your way.