The common causes of stomach pain include infection, constipation, peptic ulcers, hernia, gallstones, appendicitis, food allergy, lactose intolerance, acid reflux disease, and food poisoning.

Immediate medical attention is required if:
-The pain is extreme and does not reduce or is recurrent
-The pain is a consequence of a recent injury
-The pain is accompanied by chest pain
-Your stomach is tender to touch
-You are pregnant

Medical attention is required if the following symptoms are present along with stomach pain:
-Fever
-Severe vomiting
-Dehydration
-Increased urine frequency, dark-colored urine, painful urination, excessive thirst
-Constipation
-Blood in vomit or stools
-Difficulty breathing
-Swollen abdomen
-Yellowish skin discoloration

Your doctor will ask you a bunch of questions to rule out the cause of pain along with physical examination. He will further advise tests based on his observation and analysis, which may include:
-Blood, urine, or stool tests
-X-ray
-Ultrasound
-Barium swallows or Enemas
-Endoscopy
-CT scan
-MRI scan

The different types of abdominal pain include:
-Localized: Limited to a single area commonly seen with stomach ulcers
-Cramp-like: Linked with flatulence, constipation, bloating, or diarrhea associated with menstruation, miscarriage, or any complications related to female reproductive organs
-Colicky pain related to an underlying severe condition, which includes kidney or gallstones