Depakote and the liver

My 7 yr. old son takes 1000 mg. of Depakote daily for  his epilepsy and has been on it at that dose since March.  He's had two blood tests with the last one in April.  His liver tests were fine.  What concerns me is for nearly the past three weeks his stools have turned very light in color - cream colored.  He has no other symptoms other than stomach discomfort after eating, but I feel that may be due to overeating.  The Depakote has increased his appetite such that he's gained 18 pounds since March (he doesn't gorge on junk food, but just can't get satisfied).  

I spoke with his PCP's and Neuro's office and they said unless his stools were snow white or he had yellow eyes not to worry.  The neuro's office also said that since his liver tests were fine in April then he wouldn't be having liver problems now.???

My concern is that this may be a sign of subtle changes taking place in his liver due to the Depakote.  I can find an explantion for changes in color of stools (dark, green, yellow), but not when they become very pale.  Could this be a liver problem?

Thank You,

Dee