J.S.
My pediatrician wanted my babies back to their birth weight by 10 days to 2 weeks old. My kids all lost a pound right away, but gained it back by 10 days and then went on to nurse for over a year.
Right now your daughter is less than a week old. You are doing great. For me, being engorged and having more milk than my babies needed the first few weeks was normal. I was always able to express more than they could eat the first few weeks. Keep nursing on demand (every two hours or more if she wants too) and taking your vitamins.
Don't offer her the formula if she is nursing regularly (every few hours) and has wet diapers (8-10 per day).
If you are worried about her consumption, ask for a weight check at the doc's office. With my third they had me come in, weighed her (naked) then I nursed her and they weighed her again to get an accurate idea of how much she was eating (in oz.). It was reassuring, and I can imagine for a first time nurser that would be very nice information to have.
You are doing great. Go to the doc. about your infection, and get antibiotics, but make sure you tell them you are nursing.
J.