My 6 week old has gone from sleeping on her back in the cot a few times in 24 hours to now not wanting to be put down- unless she is playing. I'm exhausted and have to sleep upright with her breast feeding most of the night. This is my 3rd child and the other 2 improved in their sleeping habits at this stage. Anyone else experienced this?if so how did you handle it and how long does it last?