Suggest Treatment For Bilateral Foot Pain

Hello, I have a 5 year old who has been having episodes of bilateral leg and foot pain, this has been happing since he was 15 months old, again it s on and off type of pain. Usually flares up when he has been active, and pains are usually at night, but he has been having pains during the day as well. He has been to PT and that seemed to help some, but he still experience the pain. we were told that he has flat feet, which I ordered insoles for his shoes, denexpecting those to come in. I am concern that this may be more than just flat feet, should my son have a blood test to check his calcium, or hemoglobin level?