Testicular pain is caused by many different causes other than swine flu and it does not seem to have any relation with it. Testicular pain can be due to injury, infection (Epididymitis or Orchitis) or inflammation, testicular torsion, excessive bicycle riding, hernia or kidney or ureteric stones. The final diagnosis can only be made after a thorough physical examination including examination of the abdomen, scrotum, testicles and rectum.
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 sincere advice is to consult a urologist.
I hope it helps. Take care and regards.