It could easily be all of the above My DS started waking up every hour at 24 weeks old after doing 10 hour stints at night. I figured it had something to do with the realisation that I *could* leave, so he wanted to make sure that I didn't. Co-sleeping can help when you're starting to feel really wrecked, if your DS is missing you and needs more comfort then he might go back to sleeping longer once that need is fulfilled? I always slept in-between DS and DH, so DH could roll around as much as he liked, and DS could roll around as much as he liked too!

Good luck, it's tough when they change so quickly, especially when you are going through a big change too!