What Causes Persistent Pain In Abdomen Along With Nausea In A Child?

Hi My son has been suffering with stomach ache and nausea for the past week. He is 6 years old and the doctor has prescribed him junior lanzol for 6 days. Today is the fourth day and he is still complaining of pain. Also gave him Cyclopan. He is still complaining of pain and even nausea hasn t come down. What do I do now.