My daughter is 8 weeks old and the past few days she has been sleeping a lot more during the day too so I think it's probably a growth spurt. She just started sleeping through the night a few days ago, she goes to sleep between 9-10pm and sleeps until 5-6am but before that she was up every 3-4 hours. I thought she would never sleep through the night because, like you, I was spoiled with my first who slept through the night at 4 weeks and would sleep 11 hour stretches!
I think the reason my daughter is sleeping so much at night now is when she does cry in the middle of the night I give her her pacifier just to see if she will go back to sleep and she does right away. So yes she is still waking at night but instead of picking her up right away, I see if she will go back to sleep if I give her the pacifier, so maybe if your baby takes a pacifier you can try that? My first slept through the night so early because we had him on a routine of bath, bottle, bed every single night and it worked really great for him, but we haven't done that with this one yet because it's a lot harder for us to be consistent when we have a toddler running around. Good luck!