IBS, or irrritable bowel syndrome, is a difficult disorder to treat. For many years IBS was believed to be a psychosomatic disorder caused by stress. However in recent years there has been some research on the connection between the digestive tract and the mind centering on something called the "brain-gut axis", a body/mind feedback system which scientists theorize may become derailed after an intestinal injury or infection, causing IBS in some patients.
Currently most of the successful treatments for IBS have come from alternative therapies, so acupressure is a reasonable thing to try. Here is an article which describes some of the acupressure points associated with the digestive system. Also keep in mind that IBS is very closely linked to high stress levels, so trying to take care of yourself emotionally is worth the effort; gentle exercise and meditation would be good adjuncts to acupressure.