it could be a few things. The first thing that comes to mind is a torsion, though you should be feeling inflammation in your vas deferens (which is the tube connecting your testicles to your prostate). If this pain continues, though, I would go and see a doctor about it, just because random pain in the testicular region could be a variety of things. It's not necessary to come to the conclusion that it's cancer until you've been properly examined... it's stressful!