Thanks for your query,
Loose motions are usually viral in origin and it takes few days to get settled.most important thing is to maintain proper hydration,give oral rehydration solution after each loose stools,give plenty of water,coconut water,curd,banana,boiled potato,u can also give rice with curd,kichidi with curd.
his appetite will increase slowly.in the meantime continue with paracetamol
is above 100F
you can also give lactobacillus
sachet for 2 to 3 days,there is no need of giving antiallergy syrup,
Your son will be fine.