Benign Prostatic Hyperplasia (BPH): Given the patient's age and symptoms of difficult urination for years, BPH is a highly likely cause. The normal PSA level does not rule out BPH, as PSA can be normal in many cases of BPH.

Chronic Prostatitis: This condition can cause deep abdominal pain and urinary symptoms similar to BPH. The absence of neurogenic bladder and normal PSA makes this a plausible diagnosis.
Overactive Bladder: Although not directly related to the deep abdominal pain, overactive bladder can cause urinary urgency and frequency, contributing to the patient's difficult urination.
Abdominal Obesity-related Issues: The patient's abdominal obesity could be contributing to the urinary symptoms, possibly due to increased pressure on the bladder or urethra.

Prostate Cancer: Despite a normal PSA, prostate cancer cannot be entirely ruled out without further evaluation (e.g., digital rectal exam, biopsy if indicated). It's crucial to consider this diagnosis due to its potential severity.
Bladder Cancer: Although less common, bladder cancer can present with urinary symptoms and abdominal pain. Given the patient's age and symptoms, it's essential to keep this diagnosis in mind.
Kidney Stones: While the patient does not have typical symptoms like flank pain or hematuria, kidney stones can sometimes present atypically, especially in older adults.

Interstititial Cystitis: A chronic condition causing bladder pressure, bladder pain, and sometimes pelvic pain. The symptoms can overlap with those of BPH or prostatitis but are less common.
Bladder Outlet Obstruction due to Other Causes: Such as urethral stricture or bladder neck contracture, which are less common but could explain the patient's symptoms.
Neurological Conditions Affecting the Bladder: Such as multiple sclerosis or Parkinson's disease, which could cause urinary symptoms. However, the absence of other neurological symptoms makes these diagnoses less likely.