Urinary Retention with Overflow Incontinence and Possible Urinary Tract Infection (UTI): The patient's symptoms of urinary straining, hesitancy, decreased amount of urine, and the ability to urinate only after defecating suggest urinary retention. The presence of infection signs in the initial blood test and the prescription of antibiotics support the possibility of a UTI. The intermittent abdominal pain, especially if localized to the upper epigastric region, could be referred pain from the urinary system.

Gastroenteritis: The patient's symptoms of diarrhea, abdominal pain, and malaise could suggest a gastrointestinal infection. The fact that the patient was prescribed antibiotics on two occasions implies that an infectious cause was considered.
Prostatitis: Given the patient's age and symptoms of urinary retention, hesitancy, and straining, prostatitis is a possible diagnosis. The abdominal pain could be related to the prostate infection.
Diverticulitis: Although less common in this age group, the patient's symptoms of abdominal pain, changes in bowel habits (diarrhea), and possible signs of infection could suggest diverticulitis, especially if the pain localizes to the left lower quadrant.

Appendicitis: Although the pain started in the upper epigastric region, appendicitis can sometimes present with atypical pain locations, especially if the appendix is retrocecal. The severity of the pain and the presence of fever (implied by the signs of infection) make appendicitis a diagnosis that should not be missed due to its potential for serious complications if not treated promptly.
Kidney Stones: The patient's severe abdominal pain, urinary symptoms, and possible infection signs could also suggest kidney stones, particularly if the stones are causing an obstruction. This diagnosis is critical to identify due to the potential for severe pain and complications like sepsis if an obstructing stone becomes infected.
Abdominal Aortic Aneurysm (AAA): Although less likely given the patient's age and lack of specific risk factors mentioned (like a significant smoking history or known vascular disease), AAA can present with abdominal pain and should be considered, especially in older males, due to its high mortality rate if ruptured.

Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease or ulcerative colitis could explain the patient's chronic abdominal pain, diarrhea, and weight loss (implied by general weakness). However, these conditions are less likely given the acute presentation and the patient's age.
Pancreatitis: The upper epigastric pain could suggest pancreatitis, especially if the patient had a recent history of alcohol consumption or gallstones. However, the lack of specific risk factors (like recent heavy alcohol use or known gallstones) makes this diagnosis less likely.
Intestinal Obstruction: The patient's symptoms of abdominal pain, diarrhea, and possible urinary retention could suggest an intestinal obstruction, although this would be unusual without a history of abdominal surgery or other predisposing factors.