I'm sorry but I disagree with Fritzi.  Not back to birth weight by 6 weeks
is clearly starving for whatever reason.  oz gained per week has been a
minimum of 4 oz/week for as long as I can remember with most BF babies
gaining at least 7 and it has nothing to  do  with growth charts devised by
whomever.  Kathleen Detwyler gives a real  good talk  on growth charts.  Or
 read her article in the June 1998 JHL.  It doesn't matter who devised the
chart or what chart you use - the baby MUST grow, period.  This baby is not
growing and is in serious jeopardy that could lead to poor brain
development.  The cause of no growth needs to be figured out ASAP.
Sincerely, Pat in SNJ