Thank you for your question.
I am Dr. Su S. and I will try my best to help you.
The pain in the back at this age can be due to a few factors.
It can be from musculoskeletal origin; bones and muscles can be involved.
Disease of the kidney like stones, infection can cause such pain.
Motrin or Tylenol can help to reduce the pain and inflammation.
Application of warm wet towel can be soothing.
Give him more fluid.
It can help in tiny stone or mild infection.
As it is going on for a few weeks, it should be checked by doctor.
A few tests like urine analysis, scan, X-ray etc. can be taken to know the precise cause.
I hope this information will be helpful.
If you have any query, please feel free to ask.
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Wish his healthy life.