Hello And Thank You. My Son, Just Turned 11, Was

Hello and thank you. My son, just turned 11, was born w/ one kidney, Doctors determined there were no other complications, ie; one did not die off, just born w/ one. He has been very healthy, but pediatrician said sometimes when the child goes through a growth strout it can overtax the kidney. Michael has been complaining of pain in his upper center abdomen, headaches, says no problem w/ urination or constipation. But I'm concerned and would appreciate any direction