Thanks for the link mellie. That says one happens at 12 weeks, hopefully I've just had mine, with the few nights of bad sleep.
According to that, the later wonder weeks can last longer, several weeks at a time. We're all in for some fun there!
I wonder why they call them wonder weeks. It sounds kind of gimmicky like it's not a real thing.
I've got a graco car seat and we took the newborn insert out within days as it was too small straight away. After that, there's a series of slots for the shoulder straps and she's on the second highest and even then they're slightly under her shoulders. The strap length has been extended to its widest, though there's still a couple of inches adjustment left in them. If I need to, I'll take it back to mothercare and ask advice from the car seat fitting staff. She's really long, she's on the 99th percentile for length and it's mostly body, with little legs, which my mum calls 'ducks disease'!