Thanks for your query.Based on the facts that you have posted it appears that your son has developed Acute Epididymitis
(Infection of Epididymis
Please get his Routine urine test done and give him broad spectrum antibiotics along with anti inflammatory medication like Diclofenac
twice daily .
Get the prescription of medicines from your family Physician.
Ensure to drink more water.To keep his urine dilute .
It should get resolved in 2 weeks.