It looks like a virus that is going on.
Usually when kids are sick, they don`t eat well. Viral fevers can be associated with gastritis
, that can cause pain in his tummy. Medications like Lansoprazole
Be sure he drinks well.
You may give him juices, milk, porridge, vegetable soups etc.
Keep an eye on his activity.
Loose stools might be because of his excess juice intake or viral gastro enteritis
which he is developing.
If its watery and very frequent, you might have to stop his juices and milk.
In such a case rice based food items, Mashed potato, Banana, Curd , ORS
, vegetable soups etc will help. In any diarrheal illness, one must be careful that child does not get dehydrated.
Be sure he passes urine atleast 4 to 5 times in a day.
At any point of time, if he develops high grade fever, he becomes very dull or irritable, you see blood or pus in the stools, his urine frequency is very less- please do not hesitate to visit your Pediatrician
Hope my answer helps you.
Wish your son good health.