11 week old waking frequently

[Hazzy135]

My baby boy is 11 week old and recently his night time sleeping has gone downhill. Around a week ago he was doing 51/2 - 6 hours for the first stretch of night and then waking up 2-3 hours after that. However, he's not gone back to sleeping 2-3 hours before waking again.
Also we have so much trouble putting him down to sleep. He resists going to sleep any other way than feeding and will get himself so upset if we try and rock him etc. But sometimes he wakes numerous times and it takes a few hours to get him to stay down! I've tried holding him for 20 minutes but even then sometimes he only stays down for another half an hour before waking.
Tonight I noticed he was awake but not crying (just heard a change in his breathing) so thought I'd leave him to see if he'd drop off himself as he can do this sometimes and he woke me up moaning 50 minutes later so I have no idea if he slept any more in that time or not. After I fed him and put him down again he woke up about 15 minutes later with exciting laughing noises!
Any idea what's happening? Is this a normal stage? I've heard about the 4 month regression but he seems a little young for that. He has seemed to understand day and night for a while now but tonight has made me thing maybe he hasn't got it as well as I though!
He naps in his room as he's very alert and has never been able to sleep with distractions from being 2 weeks old. We reluctantly tried this after a few weeks of a very overtired upset baby! And he has definitely become aware that he's on his own when this happens... he'll sometimes cry and whinge and then smile when me or my partner re-enter.
We've also just stopped swaddling which might be having an effect. He was escaping from it every night and waking up frustrated that he couldn't move.
Any advice appreciated!
Thank you.