I recently had to deal with the same problem with my 1 year old who so far
was such a sweet little nurser. She litterally turned into a monster
overnite and would bite constantly.  Even went on strike on one side which
I tought was fear of my reaction when biting.  To make a long story short,
it turned out that the little one had thrush! took me a week and sore
nipples to figure it out.  Once the thrush was under control, everything
returned to normal.  So from now on I suggest to also look for thrush in
mouths of biting babies!

Maryelle