Why not try excluding items of food from your diet. Food allergies/intolerances can be a big cause of IBS. Also, add Metamucil. It is water soluble fiber and can be taken twice daily. This will help get more fiber into your diet.
Also, lots of gas can mean that your good intestinal bacteria are out of balance. You can rebalance by taking Acidophilus caps twice daily on an empty stomach or eating live yogurt. They contain the same things and if you reduce the gas you can also reduce a lot of your stomach pains too.
Try reducing any stress and anxiety that you are under. If you do this it can also help your stomach, due to the mind/gut link. Chemicals are released from the brain during stress that also have a significant effect on the gut, causing problems such as gas and stomach pains.
Drink plenty of fluid and eat a good all round diet.
Unfortunately, IBS can cause D/C and severe stomach pains, but it does not need to be anything more serious than this.