I am having the same problem. My LO was an excellent sleeper, but I have evidently messed it up somewhere. He wakes after 20 minutes, SCREAMING. Using PU/PD, we've gotten a little better at settling back down to sleep another 20 mins, but the CURSE of the swaddle is also a factor. At 15 wks, can't sleep without it, as his arms flail around, but can't stand to be in it, and screams as we swaddle him. He then twists, turns, strains and pushes to get out. So we're taking naptime 20 mins at a time right now, and I am at my wits end.
Nighttime sleep is better. We put him down at 8:30 and don't hear a peep until around 4 AM, when he is unswaddled and unhappy. We reswaddle and then have to do this again about 2 more times before 7 AM. Can ANYONE help us? I've read all the 45 min. nap info, but what about 20 minutes and the swaddle curse? :?