SOH - Demand feeding doesn't have to be on EVERY demand! It sounds to me like she might "snacking". Why wouldn't she be happy, we all love to snack.
It's going to be tough, but I think you might have to try a bit of tough love and make her wait and have a full meal. If she was a toddler, you wouldn't let her graze all day, would you? Obviously I'm not saying you have to set meal times, but I think you'll see where I'm coming from.
She doesn't need to eat more often than every 2.5 to 3 hours. May I suggest that you get a couple of decent meals in you (it does wonders for your milk quality within hours) and make the little muggins properly hungry. It sounds mean as anything, but I suggested it to a lady at NCT last week who was having similar problems and it worked. If she's just fed for say 10 minutes, then make her wait at least an hour until the next feed and if she feeds for longer that time, then make her wait a bit an hour and 15 mins for the next feed. If she's on and off your boobs all day, is it possible that she's not getting as much hind milk as she would if she had a longer feed?
It's worth a shot if you can bear it. The NCT lady I mentioned - her LO is going 2.5 to 3 hours now. She's also giving EBM at night so her LO feeds quicker and goes back to sleep faster.
Further to all this (which you are obv free to ignore!) and you may already know all this... Don't forget that she won't be hungry every time she cries. Even if she seems happier when you put her to the breast and even if she feeds a bit - it doesn't mean she was crying because she was hungry. I kept forgetting this at first, btw, which is why I'm saying it.
I found some of the tips in Baby Whisperer very useful, like:
If your baby is crying less than 2.5 to 3 hours after a feed, she is probably not hungry. (For me, if she wakes say, 2 hours after a feed and is crying, I certainly don't make her wait, but if she wakes 45 mins after a big feed, now I won't feed her.)
Crying from hunger will start with a little cough sound in the back of the throat then start and will build up to sound like a steady waa, waa, waa. You can look for the obvious signs of rooting (though my baby roots out of "interest"), tongue will pop out of mouth.
The cry most often confused with hunger is tiredness and overtiredness. "Starts as cranky, irregular-frequency fussing, but if not stopped quickly, it escalates to an overtired cry: first, three short wails followed by a hard cry, then two short breaths and a longer even louder cry. Usually will cry and cry and if left alone, will eventually fall asleep. Visual signs are: "Blinks, yawns. If not put to bed, physical signs can include back arching, legs kicking and arms flailing; may grab own ears or cheeks and scratch face (a reflex); if you're holding her, squirms and tries to turn into your body. If he continues to cry, face will become bright red.
Other notes on this: "Of all cries, the most often misinterpreted for hunger. Therefore, pay close attention to WHEN it occurs. It may come after playtime, or after someone has been cooing at the baby. Squirming is often mistaken for colic."
Discerning between those two really helped me. It genuinely didn't occur to me that if she'd just had a feed 30 mins ago and was crying that she was probably tired. It really didn't. I've read in a couple of different books that babies can only really be awake for about 45 mins without getting tired. That's a good indicator for me too, about what she's crying about.
Hope that helps a bit. x
Oh and you'd be very welcome to come and stay here, SOH. No "proper" beds yet, just inflatables unfortunately, but we have a spare room. The offer is there anyway. Am very willing to do a mercy-dash and fill my boot with ready meals for you, btw.
4oz is LOADS if you're hand expressing! My goodness. I only get that with the super-duper pump. You are a milk machine!