A fair number of people report that both their lower back and IBS hurt at the same time. The mechanism for this is not well studied, so it is hard to say exactly why one would flare the other up. (although it could be that spasms in one get the other spasming, or it could be that when one is causing pain it changes how you perceive the pain from the other. That is it hurts some all the time, but is much more noticable when you are already in pain)You should have your back evaluated as there may be some problem that it has all on its own that needs to be addressed. K.