First of all proper examination and investigations are Necessary bcoz this problem may have serious consequences. It may be due to epididymitis which is an inflammation of testicles, or testicular torsion or may be hydrocele, which, if so, has to be corrected surgically. So first an USG (color Doppler) scrotum is must. I will advise a proper check up by visiting a general surgeon.
An expert advice should be taken. USG scrotum should be done.