My poor 5 year old suffers nightly with sevear leg cramps. Dr just claims growing pains... HELP!?

For most of my son's young life he has suffered from mive leg cramps. Even from as young as a couple months I can recall him waking up kicking and having a rock hard calf. It seems to act up when he has been very active earlier that day. However, it has become a nightly issue and keeps him from sleep. I have talked to several doctors and they say its just growing pains. My gut says otherwise because now the pains are showing up during the day as well. Someone please help me. My poor baby is in pain and I just want to make it stop. :(