I hear your pain dusty, DD2 was exactly the same which was a complete shock to the system as DD1 always had mammoth day sleeps from a very early age. I couldn't persist with trying to resettle her as there was always too much going on - DD1 to look after as well as trying to relactate so pumping in every spare moment. So, after a few weeks with no luck with the rocking, shushing etc. etc. I finally conceded defeat and just used a dummy. Didn't want to do it but something had to give. That doesn't work every single time but does most times which means everyone is saner.

She's now about three and a half months old and in the last couple of weeks she's learnt to resettle herself so yep, I think they do grow out of it so you might not have too longer to wait before it all happens naturally.