My daughter had somethng that sounds similar..look up ''severs'' It is caused by an inbalance of the speed of bone and muscle growth and is common in sporty youngsters. We had a gait analysis done , custom orthotics , calf stretches and problem solved.
Apparently they grow out of it as muscles and bones get in sync but this may not happen until they are out of puberty.
We went to an osteopath who I have been seeing for years and who does not make hasty decisions regarding expensive orthotics so I trusted her when she advised them straight away.
Let us know!