He seems to want to be nursing constantly. I got a breast pump today and tried pumping after a feeding, and I got not even 0.5 oz. He seems so hungry that I'm considering making up a bottle of formula for him. Any thoughts/suggestions? His latch seems to be ok, but I'm guessing that my milk hasn't entirely come in yet.
Either way, I'm going crazy here! 
Re: Breastfeeding is hard.
I could totally be wrong but I'm under the impression that you'll know when your milk is totally in.
He's stimulating your milk production with his constant nursing. Has he had a checkup since y'all got home?
I would try to avoid giving him formula (assuming he's gaining), only because it could contribute to supply issues. Have you met with a LC?
It is SO hard, but you can do it. I was miserable for a while, but I love it more than anything now. Keep up the good work.
Edited for wording
Mmmm...cake!
Beabs, check this out in the meantime.
Kelly mom
If your ticker is accurate, then I think you are really doing fine. 1/2 ounce AFTER a feeding is great. That is 15ml. I wasn't getting that 5 days after birth. That was when my milk finally started to come in. It really wasn't until 7-10 days after birth that I could really see I was getting more milk. Babies truly don't need much in the first weeks of life. Their bellies won't fit a lot.
Check this out to see the size/amount a baby will eat. Really, it isn't much!
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We'll miss you sweet Debbie Girl (4.21.12) and sweet Cindy Girl (8.9.12)

They do nurse constantly in the beginning. All the nursing will help to build your supply. You can also do skin to skin to help you milk come in.
When my milk came in, it felt like I had 2 bowling balls attached to my chest. So you might not be there quite yet.
I hope your weight check goes well tomorrow and puts your mind at ease.
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I think some people start to second guess things and when you start pumping and supplementing early on it can cause a lot of problems. I would really try to hold off on the formula and the pumping right now, if you can.
They nurse constantly at the beginning because their stomachs are so small. It also helps get your milk to come in and establish your supply. Frequent nursing doesn't mean that he's not getting enough. You probably already know this, but the general guideline for nursing at this point is every two hours, counted from when the nursing sessions start.
I definitely knew when my milk came in. I woke up with rock hard boobs and they had literally grown a cup size overnight.
med-free birth x2, breastfeeding, baby wearing SAHM
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I'm one of those who didn't feel their milk come in, but the tip off was that DS finally gained a bit. I have low supply, so I'm still lucky to get .5 oz. after a feeding, and for anyone less than a week after giving birth, .5 oz. is awesome! You're doing great!
Personally, I would hold off on supplementing, but do whatever you feel comfortable with. Hang in there!
Cloth-diapering, breastfeeding, baby-wearing SAHM/grad student
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First off, I know it's exhausting but everything that is happening is NORMAL. Baby wants to nurse constantly (or feels like it), because his stomach is about the size of a shooter marble and milk digests in about 90 minutes. Getting .5 ounce after a feeding is AMAZING. Most people are getting drops at 5 days PP.
How many wet/poopy diapers is he having a day? That is the best gauge of how much milk he is getting. He should be having about 6 wet or poop diapers a day now.
Breastfeeding is a total and utter mind fvck in the beginning. If you need any support or have more questions let me know. The breastfeeding board is great too.
Oh, and if your getting .5 ounce after a feeding, your milk is in...lol