I have been experiencing some pain in my testicles, although it is slight, no swelling or other effects. i had been lifting weights. what could it be?

Strain...?: In your age most important is to recognize emergency as a" Testicular torsion" or " twist " of testicle - but it is accompanied by excruciating pain . Not just ache. Other conditions form exercise, lifting etc may occur as " groin strain" - in inguinal canal where sometimes hernia occurs may be muscle strain or hernia and may project as pain to testicle. Inflammation is other possibility. See MD