there is transient intolerance to lactose containing items. This is due to loss of epithelial cells
and hence lactase enzymes. These epithelial cells usually regenerates within few days.
This can be assessed by decreasing the lactose content in feeds and by presence of reducing substance and low pH in stool.
Lactose contain feed can also cause bloating
So I would suggest you to avoid milk and milk based food items for few days. Even juices should be avoided as they can lead to increase frequency by increasing osmolarity.
Give him some lactobacillus
containing probiotics for 3-5 days. Also give Zinc syrup. You need not to worry as recovery may vary according to individuals. Maintain hydration and proper nutrition.