As there is associated dull right abdominal pain,hence urinary infections,kidney infections ,tumors,appendicitis,worm or flukes infestation,
intussusception or
malrotation,endocrine causes
and hematologic causes like sickle cell anemia
and Henoch Schonlein purpura can be suspected.
In my opinion, your son should be seen by a pediatrician right away.Various investigations are required to confirm a diagnosis.