The most common cause of this is indirect inguinal hernia. This happens during straining, especially when
lifting heavy objects, and this can cause some part of your small intestines to get translocated in one side
of the scrotal sac.
Another possibility is fluid collection or hydrocoele. This can present with unilateral scrotal swelling that
is usually painless.
This should be assessed by a surgeon, since eventually, there would be a risk of strangulating the bowel
segment, and this can cause serious problems. If the intestine segment gets inadequate oxygen or blood
supply, this can lead to bowel necrosis and this may warrant a major emergency operation.
For now, it is recommended that you refrain from lifting heavy weights, or straining during defecation.
Regards and God bless.