Hi Fiona,
I see babies like that and my first thought -- esp.with an experienced
nursing mom (a multilacta?) -- is that there is something wrong with the
baby.  A lot of the time its a transient issue -- mild birth injury that
isn't overtly detectable, but that makes baby uncomfortable, cranky, and
mis-time suck-swallow-breathe cycling.  Perhaps this mis-timing creates
swallowing dysphasia with resultant aversion to eating.  Sometimes this is a
more persistant problem which needs to have some tests to see if there is a
swallowing disorder.  I've heard speech pathologists discribe incredible
aversion to feeding from even dripping breasts and easy-to-flow from bottles
by babies whose every swallow produces the sensation of drowning.

 Reflux can also produce these babies who won't feed even from a flowing
breast.  It hurts them to eat.  I've seen even very good pediatricians miss
reflux.  I had one RN client who worked for an excellent pedi who bfed
herself and kept an electric pump on-site for herself and staff.  The RN had
an bountiful supply and an infant who almost starved no matter what or how
she was fed..  At 6 mo pp the 2nd specialist  identified  reflux so severe
baby's throat was ulcerated.

I have also seen babes with heart defects who just wouldn't suck.

I'd probably try a nipple shield just to see what baby would do with more
palatal stimulation.  I might also try an assessment with feeding tube taped
to finger or under a shield to see how baby handles a flow of liquid.  I'd
use a small tube and hold baby in rather up-right position so that if s/he
struggles with flow rate it won't be hard to drool out excess.  I'd also look
at tone of lips, tongue, jaws, facial symetry, etc. to see if there is
 anatomical weakness.   Sometimes just getting some weight on these babies --
no matter how you do it -- is the best bet.  Their sucks sometimes magically
improve just from getting more energy and recovery from birth.

Hope this helps.

Barbara Wilson-Clay, BSE, IBCLC
priv. pract. Austin, Tx