Looking for possible cause and suggestions on how to treat

My son age 17 was in the hospital  in the beginning of the month with a CPK count of 40115  ALT of 135 and AST of 515. He was told he had viral myositis upon discharge but all of the viral panels they have taken came back negative except  Mononucleosis which came back positive and he had just started taking Tricor 48mg  for 2 days before going in to the hospital. He also had a few mosquitoes bites the week before. His CPK counts are now back to normal. However his AST score was 70 on the 9th and his ALT was 109. He was retested on the 18th and his AST is 64 but his ALT went up to 141 again.   My question is what caused all of these numbers to be so high.  He was tested for  Hepatitis and the results came back negative. He also tested negative for West Nile Virus.

He is currently having back pains, headaches and fatigue. He wa not having any headaches or backpain for the last 2 weeks but these started again yesterday.

I am afraid he is going to have damage to the liver.  What should I do to help him get better.?  Are there any tests the doctors can do it find out what is causing these scores to be so high?