There are three kinds:
No one knows exactly what causes IBS. Some researchers think IBS is caused by changes in the nerves that control sensation or muscle contractions in the bowel. Others believe the central nervous system may affect the colon. And because women are two to three times more likely than men to have IBS, researchers believe that hormonal changes also play a role. IBS triggers can range from certain foods, medications or emotions. E.g. chocolate, milk and alcohol might cause constipation or diarrhoea. And the least bit of stress might send your colon into spasms.
IBS generally comprises of both dietary and psychological factors so the most effective solution should comprise both approaches. Initially, you should first of all visit your doctor for a proper diagnosis. Ask yourself if the discomfort seems to follow any pattern and, if your doctor agrees, experiment.