Denise, this scenario sounds like several I've run into this last year.
 All the suggestions about tests for mom, sound great.  I, too, would
recommend an endocrinologist.
     However, your sense of something not being right keeps nagging me.
 That's how I felt with these babies I saw (3 diff cases this year).  In each
case, mom and baby presented at several weeks old, up to 6 wks, with a hx of
FTT, slow gn, etc.  With each case Mom's milk had been suppressed to just
drips, and infant's suck was so disorganized, weak, etc it was nearly
impossible to do a digital suck evaluation.  So each mom was sent home to
pump and finger feed initially (using bm & the other stuff).  Wanted to get
some weight on these kids, and see what happened when they were getting
calories.  At 1 week, infants all gained well, milk was increasing in Mom.
 With the first case (wish I could show you the pictures!), the baby was 6
wks, l lb. under birthwt at initial visit.  Would 'suck' all day long, but
was  quite literally skin and bones.  Ped had mom giving 1 4-oz bottle of
milk per day.  Was only stooling 1x/wk, no wet diapers in 24 hrs prior to
visit, but Ped, tho concerned, told mom some bf babies just are like that.
 At 7 wks, baby had gained a pound, even tho she was only taking in about 1/2
of milk I recommended.  Suck still very disorganized.  Only took in 5cc after
20 min at breast.
I started noticing a couple of things - she really fussed when put to 1side,
and would not lift her left arm up past shoulder level.  I had arranged for
my Fam prac/PA husband to be home this time, and had him do a general neuro
ck.  He said she was within 'normal' limits.  I sent Mom home still
pumping/finger feeding & suggested having Ped do a thorough physical exam,
sharing the concerns I mentioned.  Ped poo-poo'ed my neuro questions, infant
'just fine', now that she was gaining weight.  On third visit, Mom's supply
up to norm, but the baby still could not access the milk - no matter how long
we left her at the breast, no matter how we tried to 'help' her (including
pumping on l breast while she was on the other).  Emily, the baby, was over
all doing great, a different baby- very bright eyed, smiling, alert, active -
which made her neuro things that much more apparent.  We did our own little
test,  lifting both arms, trying to gently bring her head back to a center
versus 'cocked' position, etc, and it was clear to mom & I that there was a
problem.  And suck training was not producing ANY improvement in suck (rare
in my experience).  I did some networking and found an Occupational Therapist
who specialized in infant feeding, called to talk to her, called Emily's mom,
she called her Dr.(not Ped) and got a referral, and we all trekked to the
appt.
     Eventually, Emily's dx was Tortocollis from birth trauma, that had not
been picked up on, and as a result all muscles/nerves on left side of body
had withered.  Therapy helped Emily make great progress, although most of the
therapy was not focused on oral, but integrating the whole body.  Emily is 1
yr old now, and doing fine.  She was not totally on just the breast w/o
finger feeding/SNS, etc till about 7 mos.  Once she began solids Mom was able
to just nurse her.
    So, Denise, I would recommend that you try and get this baby evaluated by
an OT, if possible.  Emily's mom had to pump for 4 months in order to keep
her supply up, until Emily's suck improved.

BTW, all of the mothers I've dealt with in this kind of situation have
preferred finger feeding to the SNS.  It gave them more control (if baby's
suck is weak, frequently they don't do well on bottle or SNS either); Mom's
finger feed for actual feeding, and bf whenever they and baby wish. Emily's
mom did use SNS successfully the last couple of months that Emily needed
supplementing, but she was only using it twice a day.
Also, we (Mom & I) wanted to know what kind of progress, if any, baby was
making with sucking.  The OT (after being convinced that you can't teach to
bf with a bottle, and this baby didn't like it anyway, and mom just flat out
refused), wanted Emily's feedings very controlled to help her stay more
organized.  For feedings the OT wanted Emily burrito wrapped (swaddled), and
then wrapped with 1 more receiving blanket that was centered in front and
wrapped tightly around shoulders, chest, arms area, and then to have Emily's
chin tucked down to her chest.  This worked so well, that I frequently use it
now.
 Ive found that instead of stressing the mom, that pre & post feeds relieve
Mom's concerns about baby getting enough, not knowing how much to complement
with, etc.  In these situations I send an electronic scale home with them,
with clear instructions.  As soon as possible I then start 'weaning' them off
the scale, depending on output, etc.
(In these cases, my mom's chart breastfeed intake, f/f (finger feeding)
intake, Pumping time & amts, and wet/stool diapers.)  I think that one of the
reasons these things don't stress moms in this situation is that they've felt
*so* helpless, out of control, scared, etc.  Finger feeding, pre/post feed
weighing, & charting give's them back some of that confidence they've lost
from the ' lactation failure'.  In these cases, the problem has been with the
baby, not the mom,( as of course, everyone suggests ' you just don't have
enough milk, honey'.)  So I explain that her low milk supply is her body's
response to lack of stimulation, etc.  I see as much improvement in Mom's as
I do the baby.  And when she goes to her Ped, or OT, she feels like she has
something worthwhile to contribute, out come charts, etc and she can tell
them exactly what's been happening.
Oh,in each of these situations, babies were eventually diagnosed with
tortocollis.

Sorry this is so long.  Hope it's helpful to Denise & others.

Kathe Catone, IBCLC, LLLL etc