An upset stomach, also sometimes called a stomach ache, refers to pain and discomfort in the abdominal area.
Most of the time, an upset stomach can be treated at home. An upset stomach may be settled by:
- Consuming clear liquids in frequent, small amounts
- Drinking plenty of fluids so urine is a pale yellow or clear color
- If vomiting occurs, start with small sips of water or sucking on ice chips and if these are well tolerated, try:
- If fluids are well tolerated, slowly add bland solid foods such as the BRAT diet:
- Bananas
- Rice, white
- Applesauce
- Toast, plain or with only jelly or honey if desired
- Avoid:
Over-the-counter (OTC) medications may help relieve certain symptoms associated with an upset stomach. Talk to your doctor to determine which medicine is right for you.
- Simethicone (Gas-X, Mylanta) for gas and bloating
- Antacids or acid reducers (Pepcid, Zantac) for gastroesophageal reflux disease (GERD)
- Stool softeners or laxatives for constipation
- Loperamide (Imodium) or bismuth subsalicylate (Pepto-Bismol) for diarrhea
- Acetaminophen (Tylenol), ibuprofen (Advil, Motrin), or naproxen (Aleve) for cramping pain
If an upset stomach is caused by a specific medical problem, such as an ulcer, treatments for that problem can help relieve symptoms.
What Are Symptoms of Upset Stomach?
Symptoms of an upset stomach include:
- Pain or discomfort in the abdomen
- Heartburn
- Burping
- Bloating
- Feeling full quickly after eating
- Nausea
An upset stomach is usually not serious, but see a doctor if you have an upset stomach and:
- Bloody bowel movements, diarrhea, or vomiting
- Pain is severe and lasts more than an hour or comes and goes for more than 24 hours
- Inability to eat or drink for hours
- Fever higher than 102°F (39°C)
- Weight loss without trying, or loss of interest in food
What Causes Upset Stomach?
Upset stomach is a symptom of many different conditions.
Common causes of upset stomach include:
- Eating meals too quickly
- Overeating
- Consuming fatty and greasy foods
- Spicy or greasy foods
- Smoking
- Too much caffeine, alcohol, or chocolate
- Antibiotics, pain relievers, and supplements
- Gas
- Constipation
- Nausea
- Vomiting
- Heartburn
- Indigestion
- Stomach flu
- Migraine
- Morning sickness during pregnancy
- Motion sickness
- Food poisoning
- Allergic reactions
- Stress
Serious conditions that may cause upset stomach can include:
- Crohn’s disease
- Irritable bowel syndrome
- Appendicitis
- Diverticulitis
- Ulcers
- Gallstones
- Celiac disease
- Depression or anxiety
How Is Upset Stomach Diagnosed?
Most cases of upset stomach are mild and self-limiting and able to be treated at home. The cause of more serious cases of upset can be diagnosed with a patient history of symptoms and a physical examination of the abdomen, which may include palpation of the area to check for tenderness, enlarged organs, or masses, and listening to the abdomen with a stethoscope for bowel sounds.
Other physical examinations to help determine the cause of an upset stomach may include:
- Rectal examination
- Pelvic examination
- Eye examination
- Skin examination for jaundice
- Heart and lung exams
Imaging studies used to diagnose the causes of abdominal pain may include:
- Ultrasound
- Computed tomography (CT) scan
- Magnetic resonance imaging (MRI; including magnetic resonance cholangiopancreatography)
- Endoscopy
- Endoscopic retrograde cholangiopancreatography
Pregnancy should be ruled out in all females of childbearing age with abdominal pain.
From 
https://www.uptodate.com/contents/stomach-ache-and-stomach-upset-the-basics?search=upset%20stomach&source=search_result&selectedTitle=1~150&usage_type=default&display_rank=1
https://www.unitypoint.org/livewell/article.aspx?id=c2a97765-27a7-40f0-a650-59e7720d10ce
https://www.uhs.wisc.edu/medical/upset-stomach/
https://www.uptodate.com/contents/evaluation-of-the-adult-with-abdominal-pain