8 yr old w/ stomach cramps, occasional vomiting and diarrhea, low fever, sneezing, and cough for 3 days. Dr said stomach virus, but could it be flu.

Yes. Flu, influenza is a virus. Your doctor is perfectly correct.
2 different viruses. Influenza causes respiratory symptoms (sore throat, congestion and cough). Viral gastroenteritis ("stomach flu") is not related to influenza at all (other than it is a virus) and causes vomiting/diarrhea. Both can cause fevers, muscle aches, and headaches.