Gastroenteritis

Our little boy is 2. He has had gastroenteritis for the past 5 days. We have spoken with his doctor and been given the usual advise of keep fluids up and eat bland foods. What I wasn't aware of was, is that you can become temporarily intolerant to milk/dairy when you have diarrhoea/sickness. We have now stopped giving him milk but does anyone know how long it can take for the milk to fully clear his system? Has anyone experienced this with their little one before? Thank you.