Biting help please!

Hello,

My son was pretty early getting teeth--he got two bottom teeth at 3.5
months. Now he's 4.5 months and one on top came in 3 days ago. Ever
since the top tooth came in, he's been biting me nonstop. I've read
the archives for suggestions, and I've been saying OUCH and smooshing
his face into my breast until he lets go, then not letting him nurse
for a bit while giving him something he can bite. I've also been
praising him when he does latch on without biting. He only bites
while latching on, and sometimes he'll bite me 5 times or so before I
can get him to latch without doing it. My nipples are sore, and I'm
getting frustrated and nervous when it's time to nurse. :-(

Do you think he's a bit too young to understand what I mean when I say
ouch and don't let him nurse for a bit? I feel bad because he looks
scared when I do it and I know he's not doing it purposefully to hurt
me. I have been giving him tylenol and ibuprofin when he seems to be
in pain and it doesn't seem to make a difference.

Can anyone help? 3 days of tons of biting is wearing me out!

Thanks very much,
Lora