C.B.
Well, you said you have tried everything you could find, so I will just let you know the methods that I have found to work, and hope there is one that you haven't tried yet!
Of course there is the biting them back! Also, put something biter or hot, or just nasty tasting on their tongue everytime they bite! Also, that way I broke my daughter, was to scream to the top of my lungs, it scared her so bad, but she doesn't bite!
These may be hard with your job, but I sure hope you find something that helps! Everyone says it's so normal for most children to bite, but I see it as dangerous, and would hate it if my child started biting! My daughter is only 15 months old, but I broke her of biting when I was still breastfeeding her! I sure hope you find something that works for you and your son!
Good luck!