Pain on left side under rib cage
may be due
to enlargement of spleen
.It is enlarged in many conditions like
Malaria,Typhoid,Blood disorders etc
He has to be investigated with Blood tests including peripheral smear,Ultrasound abdomen.
Till then give him Paracetamol tablet,Tablet Rabeprazole with domperidone and Anti spasmodic like Dicyclomine.
If you come back with reports,i will clarify further.
Wish him speedy recovery