6 yr old has fever with no vomiting or diarrhea. Periodically complains of stomach& leg pain & back. What could be problem?

? virus. The most common cause of fever without other symptoms is a viral infection. The differential diagnosis for abdominal pain, leg pain & back pain is really too big to discuss on HealthTap in less than 400 characters. I'd make an appointment with his pediatrician to discuss all the symptoms.
Fever. Your child may have a viral illness. However, for a definitive diagnosis he should be seen by his pediatrician.