To increase your milk supply you need to nurse more, which is hard if she doesn't want to. The best way to know if she is getting milk is to listen to her swallowing, she needs to be swallowing in there. More milk coming out means she will swallow more. There should be a swallow every suck, every other suck, or maybe every 3, but this might not be enough (depends on how long she is actually nursing that way, if it is at least 5 minutes of every 3 sucks is a swallow, it probably isn't much).
I had a lot of problems and didn't breastfeed for a month starting when my son was a couple of weeks old, and lost my whole milk supply. I started back up after a month, and it took me 5 weeks to get my supply back up. I used a nursing supplementer (Medela SNS), which you put formula or breastmilk in and the baby gets that through a tube while sucking on your breast. If they are getting milk from the breast, the formula will not go down as fast (and you will still need to listen for the swallows, if you don't have the tube in the right place on your breast, or it is blocked, the formula won't go down then either).
Since you are saying she is sleeping through the day as well (not a good sign to be sleeping that much more than usual unless she is sick), and it sounds like she is having less pees and poops (at least less than you are used to), I think you need to make sure you do have enough milk. Those are both signs that you don't. You can try pumping, although that isn't really a great way to tell, although if you got a lot out before and you don't get much out now, that could be a sign of lower milk supply. If you didn't nurse or pump a lot for that month, you could have affected your supply, but you can do something about it. See a lactation consultant, they will help you a lot, and I would suggest getting a supplementer if your supply is low (they might have one). If you are hearing a lot of good swallows, then you probably are fine, but if not, or if you are still worried, get some help.