My little angel

Okay...so Dylan has been into biting lately and it is driving me CRAZY...it didn't start until we came down here to Cali and for some reason it seems it's not going away any time soon. Everyone I talk to is like, "don't worry, my kid did that too and it only lasted for 2-3 wks" That's great and everything for all of you but we're going into our third MONTH here. What the heck? Poor Aisley gets the brunt of it but she's learning to defend herself better. Lately he's been hitting, pushing, scratching and pinching too. Now that the long awaited 18 months have passed and he is eligible for nursery...we get to go too since he's been so aggressive. Ugh...it used to only happen if he was attacked first...now he'll just walk by Aisley on his way to the kitchen and grab a fist of her hair and yank, then continue walking like nothing happened...or he'll be totally playing and happy and then will just decide to lean over a bite her or smack her on the head with a remote control or something and then acts shocked when we yank her away crying and punish him...Any suggestions on how to nip it in the bud before I kill my kid or die of embarrassment at the park when he attacks a random strangers baby?