kindly check serum calcium, cpk, vitamin d3  and on examination we can suggest some more evaluations. treatment in Ayurveda is based on the cause.

At this age pain will be usually due to general weakness that's why he had been put on multivitamin. But only few nervous disorders only could be prevented by vitamin suplimentation. In siddha medicine we look through this in a different aspect. The body constitution and kutram (vatha,  pitha & kapha) play a vital role. There are causes like thathu nastam (vital nutrients) It's necessary to see him in person. So kindly consult a physician. He can he healed completely.