Toni,

This baby sounds as if he's engaging in normal 5-month-old behaviour.
 I've known lots of babies -- including mine -- who went through the
pulling away phase at around 4 - 6 months.  At this age the world is
simply more interesting than mum's breast (even at night!) .  I would
suggest ending the feeding immediately when this happens, and
refusing to offer the breast again for half an hour or so.  He'll
catch on pretty fast that pulling on the nipple means no milk.  It's
OK for mum to yelp in pain too:  sometimes this startles little ones
enough that they don't try it again.

Jennifer Landels, BA, CE
Vancouver BC