DS is 7 weeks and I do this especially at night. I change him inbetween and swaddle again. At that point he's pretty awake again. He won't feed as long or enthusiastically on the second side.
If DD fell asleep I took her and placed her cheek on my breast for a few minutes to see if she woke up wanting more. If she stayed asleep after a few minutes then I considered her done.
TTC since April 2011. DH Dx MFI in February 2012. BFP #1: 7.16.12. MMC dx: 8.22.12, D&C 8.28.12, TTC Again November 2012. DH Varicocele repair November 2012; Repeat SA showed "dramatic" improvement February 2013 (awesome!)
BFP #2: 3.26.13, EDC: 12.7.13. Anya born December 9th, 2013!
Re: When LO falls asleep on one side, do you wake up/put on the other side?