I didnt need a referal to see an osteo, just ring and book.
12 days is very young to have day and night sorted out isnt it?
I would have said maybe 6 weeks.
As for the back thing, I have heard that tummy time is good for reflux bubs, I just kept mine upright.
FWIW, for me, the jury is still out on the osteo.
I thought it worked, but then I wanted to believe that.
I am pretty sure that time is what fixed my kid.
Good luck xxx