What Causes Pain In Abdomen And Frequent Bowels In A Child?

My 8 year old has been complaining of a pain in his stomach and has been going to the toilet around 5 times a day for the last 4 days. He is eating normally and is ok in himself but I am a little concerned. A few days before this started he was complaining of severe pain in his side but that only lasted a few hours. Any ideas?