Testicular pain can be due to injury, infection (Epididymitis or Orchitis) or inflammation, testicular torsion( most common in young men), excessive bicycle riding, hernia,varicocele or kidney or ureteric stones.
Lab investigations like complete blood examination, urine examination, ultrasound lower abdomen and sometimes a urethral swab will help in diagnosis. Treatment will be started thereafter.My advise would be to consult a urologist.
I sincerely hope that helps. Take care.