Mild pain on one side of the scrotum can be due to several common causes, such as minor strain or injury, inflammation or infection like epididymitis, fluid collection (hydrocele), or a small swelling of veins (varicocele), and sometimes it may even be temporary without a clear cause. Usually, rest, wearing supportive underwear, and avoiding heavy activity can help if the pain is mild and recent. However, it is important to monitor your symptoms and seek medical care promptly if the pain becomes severe or sudden, if there is swelling, redness, fever, a lump, or nausea/vomiting, as this could indicate a more serious condition, such as testicular torsion, which requires urgent treatment. If the discomfort persists for a few days, a doctor's examination (and possibly an ultrasound) is recommended to confirm the cause.