Up until a couple months ago, I had been nursing non-stop for 6+ years. I've tandemed twice. I am always surprised how sore my nipples get once the new baby arrives even though the nursing feels super gentle. So get your ointment of choice to soothe dry, cracked nipples and remember to help your newborn have proper form. My toddlers had become sloppy nursers and I forgot how important it was to help the newborn latch properly.
Don't be surprised if your DS wants to increase his nursing too. I thought it was a handy and natural way to make my children feel secure with the presence of the new baby. They asked to nurse more and I never refused. It was pretty short-lived anyway. My DS1 would even sit in between my legs on the recliner as I nursed his little newborn brother.
I'm expecting my DD who is 2 now and weaned herself a couple months ago, to ask to nurse again once this baby is born. I've never had a child wean so early anyway, so I'm sure it would be good for her. Even my 4 year old (first born) who had weaned himself at 3 asked to try it again after his sister (third born) was born. I said "okay" and he tried for a second, then thought it was silly. I think more than anything they just want to know that they can if they want to.
One more thing that I'm sure you don't need to be reminded of, but that I forgot for a moment after my third was born, is that you have to burp newborns! Nursing came so naturally, but burping had been long forgotten by me! My DH instictively picked up the baby and burped her! Oops!
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