In terms of wet diapers, you want to see about 5-6 wet ones per day. To tell if the disposable ones are wet, you can pull apart the seat and look for yellow discolouration - but by 3 weeks, you should be able to feel some heaviness in the diaper. Poos can be every diaper to every few days - it depends.
A 3 week old should be nursing a minimum of about 8 times a day, really, so that means every 3 hrs during the day, cluster feeding of every 2 hrs in the late afternoon/evening, and maybe a slightly longer stretch overnight.
I noticed that you're giving EBM - is that so hubby can help out?
What time of day are you pumping? Just remember that when you give a bottle, even of EBM and you don't pump that feed, it tells your body not to produce milk at that time. This may or may not become a problem for you - depends how your supply is overall.
It kind of sounds like she might not be getting enough during the day, so is munching overnight, but is too sleepy to stay awake and get a full feed. Can you try to fit in another cluster feed in the evening - you can do it as a dreamfeed? So you'd feed at about 7, 10, 1 - like you are, then maybe try spacing them closer together - 3:30, 5:30, 7:30 and a dreamfeed at 10:30 (or whenever you go to bed). The times are just a suggestion - the idea is to get a few more feeds in before bedtime! Some babies even need to eat every 2.5 hrs all day long. She'll still likely need to eat once overnight (because she's still so small!), but you could see if it helps. Also, when you're feeding, really aim for a full feed, using breast compression.
Finally, most babies are more restless in the wee hours of the morning - they stir, make noise, and come slightly awake. If your snack bar is available, she'll take advantage! :wink: And if she's nibbling, even if it's not really for hunger, then she'll be less hungry during the day. You might want to consider putting a bit of space between the 2 of you in bed, so your breast is slightly less available.
Let me know how your doctor's appointment goes and how the weight is!