Tension Headache with Gastrointestinal Issues: This could be due to stress or anxiety causing both headache and stomach discomfort. The middle of the head pain is consistent with tension headaches, which are often described as a band or a squeezing sensation around the forehead, and can be accompanied by gastrointestinal symptoms like stomach pain due to the gut-brain axis.

Migraine with Abdominal Symptoms: Migraines can cause pain on one side of the head but can also present with bilateral or midline headache. They are often accompanied by nausea, vomiting, and abdominal pain, which could explain the right stomach pain.
Gallbladder Disease: Gallstones or cholecystitis can cause right upper quadrant abdominal pain and can sometimes be associated with headaches due to the systemic response to pain and inflammation.
Peptic Ulcer Disease: Ulcers in the stomach or duodenum can cause epigastric pain that may radiate to the right side and could be associated with headaches due to pain and stress response.

Appendicitis: Although appendicitis typically presents with right lower quadrant pain, it can sometimes cause pain in the right upper quadrant or be perceived as more midline, especially if the appendix is retrocecal. Headache could be a systemic response to the infection. Missing appendicitis can lead to perforation and severe consequences.
Pancreatitis: Pancreatic inflammation can cause severe abdominal pain that radiates to the back and can be associated with headaches due to the intense pain and systemic inflammatory response.
Intracranial Hemorrhage or Mass: Though less likely, an intracranial hemorrhage or a mass (like a tumor) could cause headache and, if it affects areas involved in autonomic function, could potentially cause abdominal pain.

Porphyria: This is a group of disorders that can cause abdominal pain, neurological symptoms, and sometimes headaches. It's rare but should be considered in cases where the diagnosis is unclear and other symptoms like neurological deficits or psychiatric symptoms are present.
Systemic Lupus Erythematosus (SLE): SLE can cause a wide range of symptoms including headaches, abdominal pain, and can affect multiple organ systems. It's less common but should be considered in patients with a complex presentation of symptoms.