My Mother suffered with IBS and her GP tried all sorts of things which made little difference. She suffered severe symptoms about twice a week for over 10 years.
However she is now off all medication and virtually free from any attacks. It seems it was all down to a Wheat intolerance.
My wife recently qualified in an alternative health form called kinesiology. This uses muscle reactions to do things like food intolerance testing etc. After graduationg one of her first patients was my mum and using this technique identified a wheat intolerance.
My Mother cut wheat out of her diet completely and the effects were immediate, no more attacks and no need for any medication. GP just shrugged his shoulders when she explained her improvement after changing her diet.
Not for one minute trying to promote this but a couple of sessions with somebody who practices this or something similar may help.
Do some research on the internet!