I really feel for you all. I have had the same problem here, though my DD is younger than 4 months. She went from sleeping through to waking at least 6 times a night and crying during the day. Turns out that she has reflux and is now on medication for it. Since then, she has gone back to sleeping from 7/8 till 4/5 with just one 'reinsertion of the dummy' at 3 (like clockwork ).

Just something to think about...