Appendicitis: The patient's presentation of acute right-sided abdominal pain that initially was diffuse and then localized, sharp pain that worsens with movement, and associated symptoms such as increased urinary frequency, are highly suggestive of appendicitis. The pain's progression and characteristics, along with the absence of other clear causes (e.g., nausea, vomiting, which can be present but are not universal), make appendicitis a leading consideration.

Kidney Stone (Nephrolithiasis): The sharp pain and increased urinary frequency could suggest a kidney stone, especially if the stone is causing obstruction. However, the lack of dysuria (painful urination) and the nature of the pain (which is more typical of peritoneal irritation in appendicitis) make this less likely.
Diverticulitis: Although less common on the right side, diverticulitis could present with similar symptoms, including acute abdominal pain and tenderness. The absence of changes in bowel habits and the specific location of the pain make this less likely but still a consideration.
Hernia-related complications: Given the patient's history of hernia, complications such as incarceration or strangulation could present with acute pain, especially if the hernia is on the right side. However, the description of the pain and the lack of a clear hernia bulge or specific tenderness at a hernia site make this less likely.

Ectopic Pregnancy (in a female patient, but mentioned for completeness): Although the patient is male, it's crucial to remember ectopic pregnancy in any differential for acute abdominal pain, as it is life-threatening and can present atypically.
Ruptured Aortic Aneurysm: While less likely given the patient's age and the nature of the pain, a ruptured abdominal aortic aneurysm is a catastrophic condition that must be considered, especially if there's any suspicion of hypotension or signs of shock.
Mesenteric Ischemia: This condition can present with severe abdominal pain out of proportion to physical findings and can be a diagnostic challenge. It's crucial to consider in patients with risk factors for embolic events or vascular disease.
Pneumonia: Basilar pneumonia can cause referred abdominal pain, especially if the diaphragm is involved. The patient's headache that improved with Excedrin and the absence of chest pain might distract from this diagnosis, but it should be considered, especially if there are respiratory symptoms or findings.

Ovarian Torsion (in a female patient, but mentioned for completeness): Like ectopic pregnancy, ovarian torsion is a rare but emergency condition that could present with acute abdominal pain.
Intussusception: More common in children but can occur in adults, intussusception is a condition where a part of the intestine telescopes into another, causing bowel obstruction and potentially severe pain.
Inflammatory Bowel Disease (IBD) flare: While IBD (e.g., Crohn's disease, ulcerative colitis) can cause acute abdominal pain, the presentation is usually more chronic, with changes in bowel habits and possibly weight loss. An acute flare could mimic other conditions but would be less likely without a known history of IBD.