Stomach Bug is usually affected by a virus which causes Flu
. Unfortunately the same virus can also affect the testis that mas cause swelling, pain and discomfort. Yes muskuloskeletal conditions can affect the testis by the cord that connects the testis to the ejaculaory duct is made of muscle (cremasteric muscle).
I would suggest taking it easy for a few weeks and wear tight fitting underwear. Also if testicular pain
persists or worsens I would suggest seeing a physician or a Urologist
to be sure we are not dealing with something worst.
Best Wishes to your Health.