Welcome to HCM,
First of all I would like to thank you for elaborating your question.This is the commonest complaints of this age group to me and to other pediatrician
.If there is any underline disease to cause the pain then it would obviously occurs during sleep as day time.As all possible causes are treated and all investigations are done no further things to to.
Like other patients to me I would like to assure you that its a Functional pain abdomen and here minimal treatment is required .Parents should assure that its a complex behavior of your child not a disease.
encourage him to do what he likes and "IGNORE(its process to distract him from the so called complaints) him ' his complaints ,that will cure the condition gradually.
Thanks you again.