Back injury, pain in back and stomach, soreness, bruising. X-rays, CT scan done. Treatment for pain?

My 5yr old boy fell today at school from a high bar and landed flat on his back he says. None of the teachers saw it but that is what they gathered that happened. We took him to the ER and they did x-rays on his back and ct scan on his neck . They said they didnt find anything and that he would be bruised and sore for a few days and just to give him motrin. He isnt a complainer at all and he has whined about his stomach and back hurting alot today. He is having a hard time getting up and down from sitting to standing positions. They did not do any scanning or xrays on or in the stomach area at all. They just mashed there before we left.