high alt/ast levels

I have been feeling really tired and light headed over the last few months.  I am a 23 year old male, 6 190lbs.

I went to the doctor and had some blood work done with everything normal except ALT of 157 AST of 66 and Tot Bilrubin of 1.3.

I was then tested for Hep A, B and C and all came back negative.  

After this i got an ultrasound and have a mildly fatty liver, but no tumors or cysts.

I am taking Effexor XR for depression, and although it isn't a side effect, i have read some posts of other people on forums that have elevated enzymes on Effexor.  I have been on this for 3 years and had my enzymes tested in 09 and my ALT was only 40.

Can anyone tell me if they think Effexor could be the culprit?

Can a mildly fatty liver really cause enzymes to be this high?