So is this supposed to happen between 3-4 months or from 4-5 months? LO's sleep is not what it used to be and takes him longer to fall asleep and he makes this strange strong grunt where he almost holds his breath and his face turns red, when he is tired or hungry. He used to never do that, he would just give a little cry. Hope this all ends soon.
Re: 4th month wakeful period
Check out the 3-6 month board. You'll find It mentioned many times there.
OP, I think the exact timing of the wakeful period can vary. I definitely feel like I'm going through it right now. She started STTN at 3 weeks old, but all of a sudden she's waking up every couple of hours. At the same time, I'm seeing big leaps in my DD. She's able to grab things much more easily, is way more interested in...everything, and generally seems to be developing her skills at an amazing rate right now.