A few things that might help: nursing both babies at the same time; stop relying on nursing to get them to sleep (difficult I know), if they fall asleep when nursing, put them down as soon as possible and if they wake up, use another method to help them go to sleep. A good book I read that had some perinent info about the mechanics of sleep was "Healthy Sleep Habits, Healthy Twins." There is valuable info in this book that if you don't know, will make it hard to make good decisions about how to proceed. "The No Cry Sleep Solution" is another great book, but I don't think it gives enough background info.
It really is important to catch your LO when she is just giving tiredness cues. I even went so far as to time it out. The "Healthy" book has info for how much sleep babies need and how long they can reasonably stay awake before needing to sleep. It is difficult to develop sleep routines without that info. Like, when they were newborns, I would keep track of when they woke up (tried to do everything at same time) and when an hour or so had gone by, then it was time to settle in for the next sleep period. (This kind of timing duration stuff changes as they get older of course.) I found that if I caught them before they started getting tired, they would go to sleep by themselves, much easier. Of course, one twin went to sleep much easier on her own, but if my timing was off, then it took a lot of effort and sometimes a lot of crying before they finally went to sleep. (Never left to cry it out, tho, if they were having trouble I generally rocked them.)
If you are concerned about one crying and waking another, music or a white noise machine may be helpful.Â
so sorry to hear about your back. it must be very difficult to manage. can you get someone to help at least part of the time? (Not necessarily with the sleep issues either, just in general)
HTH
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