Thanks everyone for your replies.
I'm formula feeding because my baby lost 14.5% of her body weight by day three after birth. She was getting hysterical every time I put her to the breast seemingly because she wasn't getting much nutrition from me. When we started giving her formula through a syringe (while she was latched to the breast) she calmed right down and became peaceful while suckling.
Weighing her before and after feeding sounds like a really good idea. I am looking into how to obtain a scale (don't currently have one). She definately swallows while she's nursing at the breast when she's getting formula through a tube, but I can't really tell if she swallows when she's on the breast alone. It's difficult to get her to stay latched to the breast if she's not getting the formula supplement. If she's hungry she gets frustrated very quickly with not getting enough milk. If she's not very hungry she tends to lose interest and sleep or just lay there with the nipple in her mouth, not sucking.
It's good to know breast milk can be yellow. I've been waiting for my milk to come in, hoping I would finally get a better flow then, but maybe it's already here and I'm just dealing with low supply...
I haven't had her weighed in over a week, so I don't know for sure if she's still gaining, but she looks good to me and last time she was weighed her weight was coming back up.
I want to say about pumping not being a good indicator of supply.... I would dearly love it if I was producing more than I'm able to pump, but my baby's reactions seem to suggest otherwise... ? I'll keep trying to nurse her at the breast alone (without tube feeding the formula), but it seems like she has to be in just the right mood to cooperate with me on that.
Regarding the retained placenta -- my mom had mentioned that it could be that. I've been trying to find out what the symptoms would be. So far my body seems to be returning to its pre-pregnancy state pretty quickly, so I'm thinking it's unlikely. I don't know what else I'd be looking for. I'm hesitant to go in for a check at the OB's office 'cause it's an hour away, and I'm finding long trips away from home to be very draining right now. It feels important to recharge my batteries after these last couple of very trying weeks...
Thanks again for your responses, it helps not to feel quite so alone.