Why does my stomach hurt?

A lot can happen between the time chewed-up food enters the stomach and the time it leaves the large intestine as waste, usually between 12 and 24 hours later. For starters, it has to travel through 30 feet of digestive tract, where it's propelled along by the wavelike movement of the intestinal muscles and broken down by digestive juices so that its nutrients can be absorbed into your bloodstream. Most of the discomfort you may feel during this process is due to gas that gets trapped along the way. The average gut generates a pint to a half-gallon of gas each day. Here are the main culprits.
Indigestion

You may be swallowing a lot of gas when you wolf down your food too quickly, chew gum, or take fizzy drinks. High-fibre foods also tend to produce gas because they aren't completely digested in the small intestine and end up being fermented by bacteria in the colon. That's why it's a good idea to add fibre to your diet slowly; after about three weeks your gut should adjust somewhat, and fibre-rich foods will give you less gas. Eating a lot of fatty foods can result in bloating and discomfort as well, since fat takes longer to digest and stays in the stomach longer, causing gas to build up there.
Lactose-intolerance

Some few people find that eating dairy foods can make them feel bloated and gassy. Their bodies don't produce enough lactase, the enzyme needed to digest the sugar in dairy products (lactose). When this sugar passes undigested into the colon, it gets fermented by the bacteria there and produces a lot of gas. If you suspect this is your problem, try cutting back on dairy foods for a few weeks and see if your stomach problems go away. If you're not sure, a blood or breath test can help your doctor determine whether you are lactose-intolerant.
Bacteria

The bacteria that cause food poisoning can also cause quite a bit of discomfort in your gut, even if you don't swallow enough of them to have the usual symptoms of vomiting or diarrhoea. These bacteria, such as E. coli and salmonella, find their way into many of the foods we eat, although often in such small numbers that they cause only a little extra rumbling or bloating.

Irritable bowel syndrome

Sometimes it's not the amount of gas you're producing, but how sensitive you are to it. Studies show that as little as one ounce of gas can produce spasms of pain in the intestines of people who have irritable bowel syndrome. Researchers don't know why this happens.

What can I do to ease gas pain?

Some over-the-counter products such as activated-charcoal tablets or antacids containing simethicone such as Rennie, may help break down or absorb gas. If you're lactose-intolerant, you can buy digestive enzymes to take with meals that will help you digest dairy products. A few herbal remedies may also be helpful. At the top of the list are camomile and peppermint. Many people find teas of these two varieties soothing. Camomile and peppermint teas are available from most supermarkets and healthfood stores.

When should I see a doctor?

If your stomach pain is severe or lasts for more than three days, consult a doctor. He or she may not be able to tell you exactly what the cause is; you might have some version of the mysterious collection of symptoms doctors call irritable bowel syndrome, or just a bad case of gas. But an examination can help rule out more serious medical problems. Some details are particularly telling. If the pain is brought on by hunger and relieved by eating, it could mean you have an ulcer; if the lower right side of your abdomen hurts, it might be gallstones or appendicitis