Ok, so you are getting lots of great advice.
Mama, I'm so sorry that your going through this. I think it might be a good idea to have a consultation with a lactation consultant. Considering all that you have tried already, it might be good to see a professional so you can work together to find a good solution.
I think you need to talk to your doctor about your babes decrease in wet diapers and bowels. Small, condensed, pebbly bowel movements are a sign of constipation and dehydration. See what your doctor says but I would consider giving a bit of formula instead of water.
Together with an lc and you babes ped, you can make sure that you are doing what you can to build supply and be sure your daughter is getting enough. At this point, I wouldn't worry too much about nipple confusion. But if your concerned, you could always try and SNS system.
Diane West's MMM is an amazing book that deals with many breastfeeding scenarios that indicate a decreased milk supply. Other issues that can cause decreased supply are breast reduction surgery, breast implants, asymmetrical breasts, and other breast conditions. Have you ever been to an lactation consultant? Have they ever visually inspected your breasts?
Let us know how your doing...