An elevated GGT by itself is most likely the liver, but other things can raise the levels as well. Alcohol, pancreatic disease, or biliary disease can also raise levels. Certainly the 4 grams (some are not suggesting 3 grams) of acetaminophen with occasional drinking isn't going to help.
You may want to consider abstaining from alcohol and the medication and repeating the enzymes. An ultrasound can be considered for further evaluation if the enzymes remain elevated.
Lethargy can be due to any number of liver diseases and is a non-specific symptom.
I would discuss these options with your personal physician.
Followup with your personal physician is essential.
This answer is not intended as and does not substitute for medical advice - the information presented is for patient education only. Please see your personal physician for further evaluation of your individual case.
Kevin, M.D.
Medical Weblog:
kevinmd_b