Thank you for your query.
Do not panic.
Your GP maybe right.These are signs of stomach bug.
Give him antiacid medications and mild antispasmodics for pain.
Give probiotics if he develops loose motion
Give him enery rich easily digestible food.
Check his blood and usg abdomen if the problem persists.
If you have any further queries you are free to consult me.
Hope this answers your query.
Wishing a speedy recovery.
Have a nice day.