Gastroesophageal Reflux Disease (GERD): This condition is common in adolescents and can cause sharp, intermittent epigastric pain, especially after eating. The absence of vomiting and the presence of nausea support this diagnosis.

Functional Dyspepsia: This is a common cause of recurrent or persistent upper abdominal pain in children and adolescents, not related to other pathologic conditions. The symptoms can include epigastric pain and nausea.
Peptic Ulcer Disease: Although less common in children, peptic ulcers can cause sharp, burning epigastric pain and nausea. The pain can be intermittent and related to eating.
Gastritis: Inflammation of the stomach lining can cause epigastric pain, nausea, and sometimes vomiting. Viral or bacterial infections, as well as the use of nonsteroidal anti-inflammatory drugs (NSAIDs), can lead to gastritis.

Appendicitis: Although the pain typically starts around the navel and then moves to the lower right abdomen, some cases can present with epigastric pain. It's crucial to consider appendicitis due to its potential for serious complications if not promptly treated.
Pancreatitis: This condition can cause severe, persistent epigastric pain radiating to the back, nausea, and vomiting. It's less common in children but can be triggered by gallstones, certain medications, or genetic conditions.
Cholecystitis: Inflammation of the gallbladder can cause right upper quadrant or epigastric pain, especially after eating fatty foods. It's rare in children but should be considered, especially if there's a family history of gallstones.

Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease and ulcerative colitis can cause chronic abdominal pain, diarrhea, weight loss, and sometimes nausea and vomiting. Epigastric pain is less common but can occur.
Hepatitis: Inflammation of the liver can cause right upper quadrant pain, nausea, and sometimes epigastric pain. It's less common in children but can be due to viral infections, autoimmune conditions, or drug-induced liver injury.

Can you describe the pain in more detail? Is it constant or does it come and go?
Does the pain get worse or better with eating?
Have you experienced any other symptoms like fever, diarrhea, or difficulty swallowing?
Have you recently traveled or been exposed to anyone with similar symptoms?
Do you take any medications or supplements?
Is there a family history of gastrointestinal diseases or other relevant medical conditions?
Have you noticed any relation between the pain and your menstrual cycle (if applicable)?