If this makes no sense, forgive me - my brain is mush. 
DS, 17 months, isn't sleeping. He's an active, intense, spirited kid - we've had issues before, but solved them by starting EC and a bedtime routine, and quitting baths before bed. This is new.
He has always been a night owl, staying up with us (we co-sleep) and sleeping in. Something like asleep by 10, awake by 10, with a 1-3 hour nap mid-afternoon. Ideally. This requires about a half hour of parental prep (feeding pets, brushing teeth, gathering diaper parts, etc.) and an hour and a half once in the bedroom (for him to potty, play quietly, read books, get diaper on, read final book while nursing, nurse to sleep for about 30 min. with lullabies).
LATELY we have nights where he fights sleep, repeatedly getting out of bed, and dragging things out until much later. New normal looks like finally falling asleep by 12 or so, then waking several times a night, tossing and turning, talking and nursing for at least 30 min. each time! He ends up with MAYBE 4-5 hours sleep, then is up for good by 5:30! He just passed back out at 8:30 am for a nap, but often if he takes a morning "nap" (really missed nighttime sleep) he won't take another one in the afternoon. We are talking maybe 8 hours total sleep for him, about 5 for me, dark circles all around. HELP!!!
I think we may be missing his sleep window, and then he can't settle himself down - but the other thing is, when he stays up this late, often the last thing he does before sleep is poop (sometimes asking for a snack just before)!! Could that be keeping him up? How do we reset that timing?
Getting Sleepless in America from library today.
I often chalk this up to teething (with sore nipples to prove it!) but it's become constant...even with teething tablets and advil.
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