Thanks so much for your replies everyone. I really, really appreciate the support!
The LCs and lactation docs did check her out for tongue tie, which she does not seem to have (although the LCs were uncertain as to whether or not she might have a mild case, the doc said that it is not a problem, based on my nipple shape after feeding). However there could be something going on with how she gets milk from the breast b/c I've had pain the whole nursing relationship. No one can pinpoint why, though, which is why we are currently treating for yeast (hoping that this is the root cause of the nursing pain) - but I'm not sure if yeast can affect how much she eats when she doesn't have any of the white patches in her mouth? So maybe there is something else.
I thought I'd update briefly - we are now about 17 hours into an exclusively pumping/bottle feeding/measuring experiment, and the numbers are:
total pumped so far: 23 oz
total eaten by LO so far (offered a bottle any time she was fussy, even if she just ate, and kept offering milk until she stopped drinking it, even if she finished a bottle): 25.25 oz
So even if I only get a few oz per pump over the rest of the pumps, I'm clearly making "enough" milk based on the average of about 24 oz per day, however, my pumping output is not quite keeping up with what we can get her to drink (can you get a baby to drink "too much" just by repeatedly offering more milk too often or in too large quantities?). Before bed, she drank 7 oz in a period of 2-3 hours, and first thing this morning she drank 6 oz again, and then 4.25 oz three hours later (and might have drunk more, but I'm out of pumped milk!). I thought 5 oz was about the max for all babies, and she is only 5 weeks (although she is on the taller side and had a larger weight at birth - both my husband and I are really, really tall).
I also noticed that I got a ton of milk out at the first pump (6.75 oz), but less in subsequent pumpings (closer to 4 oz) and even less in the last two pumpings (2-3 oz). This makes me wonder if I always get such a large pumping amount b/c she is not emptying the breast efficiently when she eats (but when I pump for 24h straight, there isn't this leftover milk at subsequent pumpings?). Or is it possible that my breasts are responding less and less well to the pump as the 24h stretch wears on? (I thought I usually got the most milk out in the am, but during this 24h period, that's when I got the least amount from my pumpings...) I know that I've read that the pump isn't as good as a baby at removing milk, but I'm wondering if that is equally true for all pumpings, or true for our LO?
We'll see what happens, but I'm beginning to suspect two possibilities:
1) Maybe she is getting an average amount of milk, but she actually needs more than average? (She's always been really fussy before bed, and since I cluster feed her 2-3 times before bed, I never imagined that she might be hungry, but since last night she drank 7 oz in one long feed from the bottle, I'm beginning to wonder if my breasts just aren't keeping up with a peaking evening/night demand...)
2) Maybe she is just not getting enough out at a feeding, even though my supply (based on pumping numbers) seems "fine?"
I will call the lactation doc and see what she thinks, but I was planning to add in some extra pumpings today (to try to make up the fact that she is eating more than I pumped over the last 6 hours!) and to try to rent a scale so that I could do the weighing thing over the next 24h to see how much she is eating at the breast.
I was wondering if the weighing shows that she is eating less from the breast than the bottle if I should start pumping after every feeding and then trying to get her to take a bottle after the breast. I don't know if what she has been eating from the bottle this 24 h is an accurate representation of how much she actually needs. I'm hoping the lactation doc will have helpful ideas - I'll post when I hear from her, in case my experience is helpful to anyone else...
Thanks again for all the support and advice - I really appreciate it. This is so stressful, b/c I feel so responsible for making sure she is getting enough to eat (and I can't help feeling that if she isn't getting enough to eat, that it is my fault for not taking care of her properly - I know that is silly, b/c we are learning, but I feel it nonetheless...). And there is just something really horrible about the idea that your child might be starving! :( It really helps to have helpful support and encouragement. :)