Breastfeeding questions!

C 🖤
Hello, a few questions :)
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Just wondering how to really tell the difference between nursing for hunger and actually feeding. What are the tell-tale signs for both? Does the baby take in milk while nursing for comfort or not? My LO has reflux so we sit him up for roughly 20 minutes after every feed- would be good to know when he's not really taking in any (or as much) milk to skip this out of possible!
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Also, I have to be away from the baby tomorrow evening for several hours for the first time so I've been expressing over the last day or two to make sure he's covered for the whole time I'm gone. Problem is I'm not really getting a lot when I'm pumping- is there a time in relation to feedings that's best to pump? Also, can pumping effect how much milk your baby gets during a feed?
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Finally, any tips on a good feeding routine? He's breastfed on demand and right now he usually stays on the breast for around 5-10 minutes, then we burp him, he has another 5-10 minutes, gets burped again, sits up (and usually falls asleep) for 20-30 minutes, then has a nappy change, then gets put to bed, BUT the nappy change wakes him up half of the time and then he wants to nurse again, which means the whole routine starts again. We can't do the nappy change straight after feeding because laying him down that soon makes him sick, and he also usually fills a nappy during or just after feeding. It's getting pretty draining being up for up to two hours at a time! 🙈
Thanks