A pulled muscle, trapped wind, ovarian cyst, Crohn’s disease, ulcerative colitis, constipation, duodenal ulcers, appendicitis, cholecystitis, kidney stones, cholecystitis all can pain
on the right side
. Since it has been persisting since such a long time it is best to get investigated. A complete evaluation and investigations like ultrasound abdomen may help in detecting the exact cause. Do keep us posted.
Best of luck and regards!