Don't rule out possible hernia. Has he had a Clamydia test done?
Hello and hope you are doing well.
The common causes for testicular pain are injury, infection and torsion. Injury can cause a tear of the testicular layers or it can cause a hematoma (blood collection). Infection can affect and cause epididymitis or orchitis resulting in pain. Testicular torsion is an emergency as the blood supply may be compromised and needs to be relieved. Sometimes a tumor of the testis can cause pain. Consult your primary care physician for therapy. If the need arises he may refer him to a urologist. In the meantime provide support to the scrotum, apply ice over the painful area and he can take OTC Tylenol (acetaminophen) for the pain.
Hope this helped and do keep us posted.