Based on my experience I would say anxiety is at the root of IBS. I used to have horrible problems with my IBS but once I joined a cbt group and gained the upper hand on my anxieties my IBS literally disappeared and has never come back. I would recommend trying to find a cbt program in your area or try Lucinda's which I never went through but is based on cbt principles. If you are really motivated you can do the cbt exercises on your own through books, but you have to be dedicated to doing them if you want to get relief. The book Been There, Done That? DO THIS! by Sam Obitz is the one we used in my cbt group and it is an easy book and outlines the thought countering exercise called the TEA form which is what has been instrumental to my recovery. I hope this helps and I hope you find something that works for you because IBS is really a pain on top of all we have to deal with anyway.

People with IBS should know how to manage their stress. Is there institutions that specializes on counseling the IBS sufferers?

That's a good question about places that specialize specifically for IBS? There may even be a subsection of cbt treatment that deals specifically with IBS, but I don't know of any personally. I think this is a vital component of any IBS treatment plan