welcome to healthcare magic forum.
the mainfunction of testicles is to produce sperms which is vital for child production.
whethever your testicles are performing well or not,you have to undergo semen examination.
so get your semen tested at good pathology lab with instruction of your physician.
the report of semen testing will tell you status of function of your testis.
if report is normal,feel happy & don't worry about size of testicles.
but if report is not normal consult urologist
I think my answer has satisfied your query.