Biting

We got through Wylie not eating enough and not gaining weight in the first six months of 2007. We got through Wylie having recurrent ear infections and antibiotics in the first two months of 2008. I'm not sure I can handle the latest issue. BITING. He's only biten me twice in his lifetime. 1. Once while nursing which caused a major scream from me and I promptly removed him from me and Wyatt took him while I recovered. He didn't try that again! 2. About 1 week ago he leaned in for a hug and took a bite out of me on my chest. It wasn't agressive, it wasn't mean, and I tried to not react in a manner that would either encourage or scare him. I held his face, told him we don't bite and then put him down. I then encouraged hugs, kisses and positive signs of affection. What I am facing: 1. Friday --He bit four kids at school. One on the bottom! In most cases it was because they were all on the slide and he wanted to be on it too. 2. Monday --He was the ideal child, happy, adjusted, no biting, very hug friendly to all children at school. 3. Tuesday--Bit a teacher. Not just any teacher but one he REALLY REALLY LIKES. She held his face, told him we don't bit, and then re-directed his play elsewhere. My current theories: 1. He's starting (finally) to go through some type of separation anxiety and this is the outlet. 2. His molars are coming in. We can actually see the bumps and they definitely hurt. 3. He means to kiss/hug but gets in and goes for the bite! 4. We weaned several weeks ago due to bouts of antibiotics. Is he reacting to that? What I am feeling: WHAT ON EARTH HAVE I DONE WRONG? I try to offer him the most nurturing environment. I hug him, encourage positive behavior, suggest safe and good behavior (holding hands when going down stairs, holding hands when walking on side walk, brushing teeth, sitting on bottom when drinking or eating). I give him enough independance and praise him for being independant. I try to let him work through certain acts (putting shoes on, picking up toys, opening and closing his drawer ) without doing it for him which allows some frustration on his part but also learning. If he seems overwhelmed I step in and help. WHAT HAVE I DONE WRONG? Why is he biting? None of the books or websites have advice as to why and I'm doing what they suggest. I cried on Friday on the way home and again on Tuesday. HELP!