Post splenectomy(2 month)have left upper quadrant pain radiate to back,doc ask for ct,ct show 2.5 cm nodule compatible with splenules, is pain common?

Yes, it's common: Post-splenectomy, especially if traumatic spleen injury was involved initially can result in "splenosis" where autotransplantation of splenic tissue from a damaged spleen can see elsewhere on the peritoneal surface and cause pain. I am unsure about the circumstances of your splenectomy, and your medical history related to your spleen would be helpful to know.