I've got lots of questions for you.
First, are there any health issues I should know about? How was her delivery?
Second, how often is she pooing now? Every day? More than once a day? A poo "counts" if it's as big as a 50p piece ... When did she stop making meconium?
Third, how does she seem? Is she happy, unhappy? Is she alert (for a tiny baby)? Sleepy? Miserable? How much does she sleep?
Fourth, how often are you feeding her? Are you offering both sides? How long does she feed for? How do the feeds generally end? (Does she come off? Happy? Unhappy? Does she fall asleep? Do you take her off?) Do feeds hurt? How are your nipples?
Fifth, is she feeding much at night? Where does she sleep? Does she sleep much in the daytime?
Sixth, what weight was she born at? Were all these weighings done naked, with electronic scales?
It's worth noting that we don't know what happened between day 9 and day 17. Maybe she lost even more weight, and then gained it back quickly.
Expressing after every feed can help to boost your supply. Expressing isn't a good indication of how much milk there is, though, because no pump is as effective at extracting milk as a baby is - millions of years of evolution beats some blokes in a lab, every time!
I know your midwife has looked at the attachment, but frankly, many midwives are not great at that - if you are willing to say where you live, I can have a dig for bf groups where you can go see someone who specialises in breastfeeding, who can double check your latch, and give you great support. (free!)
Alternatively, if you look at your nipple after a feed, that can give you an idea how good her latch is - your nipple should look pretty much the same as it did, going in. If it is at all smushed or crushed or different-shaped, then there is room for improvement in the latch.