Make an urgent appointment to see your doctor.
There is not enough information to even guess what the problem may be and you have not said how long you have had this for and if you have any other symptoms.
If you start to feel it is getting worse, you get a fever, feel nausea, vomit or get loose stools, get someone to take you to the ER or telephone a medic for advice.
First guess is to rule out hernia. You need to get an in-person evaluation because if an intestinal; loop is pinched, instead of a minor surgical procedure you end up with a colostomy for a year while the bowel, re-section heals.