It could have happened because you do not exercise regularly. A day's sight-seeing could have been stressful. Anti-inflammatory medicines could give you some relief. You can also apply pain relief oitments or sprays. Do not massage
. It will be better for you to consult a local doctor and get clinally examined.
Sometimes such symptoms can arise due to inguinal hernia
. Inguinal hernia occurs when a tissue gets pushed down through a weak spot into your groin causing pain and discomfort. But since you do not complain of any bulge or swelling the probabilities are low but physical examination by a doctor should be done. Later it may complicate and get strangulated to increase the ailments. It happens after weight lifting, some heavy work, coughing or straining, etc.
Treatment is repair by surgery but if the hernia is small it can be pushed back. If painless it may not need repair. Have a good day.