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.
As there is no swelling or inflammation or redness of the scrotal sacs, so the chances of epidiymitis or orchitis are rare.In testicular torsion,there is severe sharp pain and it becomes a medical emergency. 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.Hernias,varicocele and kidney or ureteric stones have to be ruled out.
I sincerely hope that helps. Take care. Please do keep me posted if you have any further queries on the same.