My son is suffering from pain in back portion of...

What is the possible causes of your son medical condition ?
it depends on the severty of the current symptoms and the other accompanied symptoms , but the common cuases are :
1. head injury 
2. flu
3. infection
4. migraines
What to do next ?
1. consult an pediatric doctor as soon as possible 
2. do the following examinations :
- physical tests 
- blood test
- CRP 
- urine test
- chest X-ray 
What is the possible treatment options ?
1. pain killers such as ibuprofen orally or IV 
2. antibiotics such as amoxicilin
3. medical observation for 24 hours