Urethral stricture: Given the history of balanitis and symptoms of urethral pain and burning on urination, a urethral stricture is a plausible cause. The previous inflammation from balanitis could have led to scarring and narrowing of the urethra.

Prostatitis: Although the patient denies being sexually active, prostatitis can occur through non-sexual means, such as bacterial infection or trauma. Symptoms like urethral pain and burning on urination can be associated with prostatitis.
Urethritis: This condition, characterized by inflammation of the urethra, can cause symptoms similar to those described. It could be due to a non-sexually transmitted infection or other irritants.
Interstitial Cystitis: A condition causing bladder pressure, bladder pain, and sometimes pelvic pain. The symptoms can include pain during urination, which might fit the patient's complaints.

Testicular Cancer with Metastasis: Although rare and less likely, testicular cancer can metastasize and cause a variety of symptoms, including pain. It's crucial to rule out such serious conditions.
Kidney Stones: While the primary symptom of kidney stones is flank pain, smaller stones can cause urethral irritation and burning during urination. Missing a kidney stone could lead to severe complications if it causes an obstruction.
Tuberculosis of the Urinary Tract: A rare but serious condition that can cause a wide range of urinary symptoms, including pain and burning during urination.

Reiter's Syndrome (Reactive Arthritis): A form of arthritis that occurs as a reaction to an infection elsewhere in the body, often in the bowel or the urethra. It's characterized by a combination of urethritis, conjunctivitis, and arthritis.
Behçet's Disease: A rare disorder that causes blood vessel inflammation throughout the body, leading to a wide range of symptoms including genital sores, mouth sores, and eye inflammation. It could potentially cause urethral symptoms, although this would be less common.