Mary,

It is very common for women to lose hair post partum.  The amount and length
of time vary greatly.  I have never seen it in print as being associated
with breastfeeding although I would suspect it is hormonal.  Anecdotally, I
lost tons of hair with all three of my children.  It lasted about 6 months
and I was sure I would go bald but never did (thank goodness).  It came out
in handfuls every time I washed my hair.  By the way, my first was bottle
fed and the other two breastfed, so the feeding method didn't make any
difference with me.

Diane Karnbach, LLLL