slightly elevated liver enzymes

[Marydale]

my 13 year old son was loosing weight, 13 lbs in 6 weeks, unintentionally.  I was concerned.  He didn't seem to have an appetite and wasn't drinking much liquid either.  One day he was so fatigued he would lay down and say he just felt better lying down.  I took him to the emergency room and they did blood tests which showed just slightly elevated white blood cells and slightly elevated bilirubin.  The emergency room doc didn't know what to make of this, so he told me to follow up with his doctor.  I did this, repeated the test, also checked for mono, cmv, hep a, b & c and some liver function tests.  The white blood test came back normal, no mono, no cmv and the bilirubin was coming down closer to normal.  The liver function tests were slightly elevated, the doctor didn't know what this meant and she told me to possibly follow up with a gastroenterologist.   My son feels fine now, eating well and drinking plenty of fluids.  I am wondering what your advice would be for this?  He is a very picky eater, no fruits or vegetables.  He now weighs 127 lbs and is 5'6 1/2"