The most likely diagnosis in this patient is epididymitis, which causes pain superolateral to the testicle and results from inflammation of the epididymis. Symptom onset in epididymitis is usually subacute, although in some patients the pain may develop relatively acutely or may be more chronic in nature. Examination is remarkable for pain that is relieved by testicular elevation. Epididymitis most commonly has an infectious cause and has a bimodal age distribution of men younger than 35 years and older than 55 years of age. Patients younger than 35 years are more likely to have sexually transmitted etiologies such as chlamydia or gonorrhea, whereas the causes in older patients are usually Escherichia coli, Enterobacteriaceae, or Pseudomonas species. This patient's presentation includes young age, history of unprotected sexual activity, subacute onset of symptoms, lower urinary tract symptoms, bogginess and pain to palpation over the superior pole of the testis, and pain relief with elevation of the testis, all clinical findings consistent with epididymitis.

Testicular torsion presents acutely along with nausea and vomiting. Unlike in this patient, the testicle would be high riding and transversely oriented, with pain that worsens with manual elevation. Doppler ultrasonography to assess blood flow is sensitive (82%) and specific (100%) in making the diagnosis of testicular torsion.

Dysuria, frequency, and urgency may accompany epididymitis and suggest the possible presence of a urinary tract infection. However, the presence of testicular bogginess and pain on examination with a lack of significant pyuria on urinalysis does not support the diagnosis of urinary tract infection.

Varicocele does not present with subacute onset, lower urinary tract symptoms, and epididymal swelling and pain. Furthermore, physical examination would reveal a characteristic “bag of worms” consistency with palpation of the scrotal contents that increases with standing and decreases when supine.