I would not just randomly treat him.
Your best bet is to have an ultrasound done and then a ultrasound guided biopsy done at the same time. This will give you the most answers. I would do this as soon as you can.
It will tell you if it is cancer or inflammation.
I also think a bile acid test may be helpful. This is a blood test that helps determine if the gall bladder, bile duct, and liver are performing as they should. It is an easy test.
I would also tun a tick titer blood test to make sure it is not Lyme's, Rocky Mountain Spotted Fever, or Erlichiosis.
For antibiotics, I would use Meteronadazole and clindamycin or a cephalosporin for now. If they took a biopsy they could also take a culture of the liver tissue to see if they could culture bacteria from it. If they did, they could see what antibiotics it was resistant and sensitive too.
The milk thistle is more for hepatic toxicity like poisoning. It would not hurt.
If it is chronic active hepatitis he will need to be on medication for the rest of his life to help the liver cells function and last longer.
There is no point in treating it as hepatitis if it is cancer. You need to have a biopsy done to figure out which one it is.