18 Reasons Why Your Stomach Hurts

http://www.health.com/health/gallery/0,,20568290,00.html
1.  swelling or blocking of gallstones
2.  inflammation of the pancreas
3.  Gastroesophageal reflux disease, or GERD 
4.  Lactose intolerance
5.  Medication side effects
6.  Inflammation of “diverticula” or pockets (Diverticulitis) that form in the lining of the intestine, usually the   colon
7.  Gluten intolerance (The most severe form of gluten intolerance is called celiac disease)
8.  Endometriosis.  Endometriosis only affects women
9.  Thyroid problems
Even though the thyroid gland is located in the neck, it can cause problems lower down in the body.
“The thyroid regulates several functions in the body and the digestive tract is one of the systems,” explains Dr. Alaradi.
If the thyroid produces too much hormone (hyperthyroidism), it speeds up the digestive tract, resulting in diarrhea and abdominal cramps, he says.
On the other hand, an underactive thyroid (hypothyroidism) slows down the digestive tract, potentially leading to pain from constipation and gas.
10. Parasites

No one wants to think that stomach symptoms are due to a parasitic worm or other creature. But it happens.
There are many types, but the most common in the U.S. are Giardia and Cryptosporidium, which you can get by swimming in contaminated pools or lakes or drinking contaminated water. (Or in some outbreaks, unpasteurized cider). The tiny protozoa cause cramps, diarrhea, and nausea about 2 to 10 days after exposure (for Crypto) or 1 to 3 weeks later (for Giardia). Other types of parasites can be picked up in undercooked or contaminated food.

11. Appendicitis

12. Ulcers

Helicobacter pylori (H. pylori) bacteria are major causes. Antibiotics and acid-suppressing drugs are often used to treat ulcers caused by bacteria.

13. Too much sugarless gum

If you consume too much sorbitol, which is found in some sugar-free products, it can cause pain and diarrhea. According to a 2008 article in BMJ, a 21-year-old woman had an 11-pound weight loss, abdominal pain, and diarrhea (as many as 12 bowel movements a day) from chewing about 16 sticks of gum a day.
A 46-year-old man had similar symptoms after chewing about 20 sticks of sugarless gum and eating sorbitol-containing sweets daily.
In both cases, cutting back fixed the problem.

14. Stress (this should list as #1 reason)

15. Food poisoning

16. Inflammatory bowel disease

Inflammatory bowel disease (IBD) is an inflammation inside the small or large intestine, Dr. Alaradi explains. It includes Crohn’s disease and ulcerative colitis.
The inflammation from IBD can cause scarring and blockage, which can lead to abdominal pain along with diarrhea and rectal bleeding. Symptoms are chronic, but can flare up and subside in cycles, making it sometimes hard to diagnose.
IBD needs to be monitored closely as it can lead to more serious problems, even cancer, later in life.
17. Irritable bowel syndrome

Irritable bowel syndrome (IBS) is not the same as inflammatory bowel disease. Although IBS can also lead to chronic abdominal pain and changes in bowel movements (such as alternating constipation and diarrhea), it is not an inflammatory condition and never involves rectal bleeding, says Dr. Alaradi.
It generally affects more women than men, is considered less serious than IBD, and can be managed through treatment of symptoms, such as pain relievers.
And unlike IBD, IBS never progresses into more serious conditions such as cancer, says Dr. Alaradi.

18. Cancer

It’s uncommon, but cancer in any one of the organs located in the abdomen—the liver, pancreas, stomach, gallbladder, or ovaries—can cause stomach pain, but usually only in the later stages, says Dr. Alaradi.
And there are usually other symptoms, like a loss of appetite, weight loss, persistent vomiting, persistent bloating of the abdomen, and recent changes in bowel habits. “If a person is used to going to the bathroom once a day and it’s changed in the past few weeks to one every three to four days, that deserves attention,” says Dr. Alaradi.

one more reason got from http://www.newhealthguide.org/Stomach-Pain-After-Eating.html is

Eating Too Fast or Overeating 

Condition Description: This is a condition where you eat too much food or eat too fast. When you eat too much food or/and to fast, your digestive system is disturbed. As a result, the food is not digested as it should be and you end up with stomach pain.

Treatments: Curb overeating. Plan all your meals and ensure that you have followed the planned timings. Always keep a bottle of water near you to keep hydrated all day. Also, do not drink water soon after eating; wait and drink it after an hour. You can take walks after eating to ease digestion.

Quick Cures for Tummy Troubles

Acupressure, tea, and probiotics can really work to cure your tummy woes.

Home Care (quoted from http://www.nlm.nih.gov/medlineplus/ency/article/003120.htm)

You can try the following home care steps to ease mild abdominal pain:

• Sip water or other clear fluids. You may have sports drinks in small amounts. (People with diabetes must check their blood sugar often and adjust their medicines as needed).
• Avoid solid food for the first few hours.
• If you have been vomiting, wait 6 hours, and then eat small amounts of mild foods such as rice, applesauce, or crackers. Avoid dairy products.
• If the pain is high up in your abdomen and occurs after meals, antacids may help, especially if you feel heartburn or indigestion. Avoid citrus, high-fat foods, fried or greasy foods, tomato products, caffeine, alcohol, and carbonated beverages.
• Avoid aspirin, ibuprofen or other anti-inflammatory medications, and narcotic pain pills unless your health care provider prescribes them. If you know that your pain is not related to your liver, you can try acetaminophen (Tylenol).

These additional steps may help prevent some types of abdominal pain:

• Drink plenty of water each day.
• Eat small meals more frequently.
• Exercise regularly.
• Limit foods that produce gas.
• Make sure that your meals are well-balanced and high in fiber. Eat plenty of fruits and vegetables.