...remember as well that they are finding more and more things that have always been misdiagnosed as IBS (esp. IBS-C) so if NOT following the diet works and the diet doesn't, maybe you don't have IBS at all but something they haven't named yet. Ever think of that?
PS. Did you ever have a Sitz marker test?
PPS. Last time we talked about this, you were eating less IF than me remember. Have you added loads more of (safe) IF in since then?