What's causing my 4yr old son's nightly leg pain?

My 4 year old son has moderate to severe leg pain every night.  This has been going on now for several months, actually starting when he was just 3 years old.  The pain is in both legs and the entire leg is involved to include his foot, but not his toes.  My sister and I had JRA (Junior Rheumatoid Arthritis) as children, with my sister's appearing at the very young age of 2 years.  With JRA there are symptoms, redness and swelling being the most common.  With my son there are no other symptoms besides the pain.  No redness or swelling.  No rash, lumps, anything.  I'm a parent of 6 children with this son being the youngest and none of the other children have ever complained of pain like this.  I'd appreciate any help I can get.  Also, I'm very concerned about giving him medication daily wondering if I'm hurting him more than helping.  

[mol6541]

If this has been going on for a long period of time it sounds like a trip to the dr is in order so they can figure out what's going on. A child having leg pain every night is not normal.