My son was 11 when he was diagnosed. He never had any aches and pains and still doesn't (2 years later). He just started going to the bathroom more frequently and having loose stools. Then he began to wake up in the middle of the night with loose stools, or sometimes even going in the bed when he was sleeping.
Please take your son to a doctor. They will probably just start out with a stool sample and a blood test to check his sed rate. And if those don't warrant further testing at least you can stop worrying about what you should be doing.