DD1, 9, just had her appendix out 3 weeks ago. Stomach ache started on a Sunday afternoon and was centered around her belly button. By the next morning it had moved down to the lower quadrant and she was walking very slowly and carefully. No fever. DH took her to the ped and she tested positive for strep and was sent home. By 4pm that Monday she was walking very gingerly, almost on her tip toes, and we knew something was up. It wasn't until later that night, when the pain really increased (she said 7 on a 10pt scale) that it hurt her to jump (it's a rebound pain). While she had no fever, she did have lack of appetite and two episodes of vomiting.
I definitely think it's worth checking out after school if it's still hurting him. DD1 didn't have surgery until Tuesday morning so while somewhat urgent, we definitely had from mid-day Sunday until 7am Tuesday without it rupturing and the surgeon said it was mildly inflamed, even after all that time passed. So I wouldn't panic, but I also wouldn't wait if it's bothering him and you don't believe it's gas or constipation.
Mom to two amazing DDs ('07 & '09) and a fur baby.
Gluten free since Nov '11 after non-celiac gluten sensitive diagnosis. Have had great improvement or total elimination of: migraines, bloating/distention, heartburn, cystic acne, canker sores, bleeding gums, eczema on elbows, dry skin and scalp, muscle cramps, PMS, hair loss, heart palpitations, fatigue. I'm amazed.