Thanks for posting your query.
With the available described symptoms, there could be possibility of acute viral gastroenteritis
is an integral prodromal symptom of viral infection.
You should consult with internal medicine specialist/ pediatrician
and should go for thorough check up.
You should also go for complete blood count
imaging, and serum electrolytes.
Viral infection has also some effect on liver and that's why loss of appetite and fatigue is very common with viral infections.
You should take complete antibiotic therapy, antispasmodics, probiotics, antipyretics.
You should maintain your hydration by taking potassium rich liquids.
Avoid milk and all milk related products.
Dr. Mayank Bhargava