Have you looked into food intolerances? I know DD1 was terrible with sleep and was able to pinpoint it to 1 food colouring in particular and I am certain other foods were affecting her. May be something to check out what you are eating and what you DD is eating, especially is something new has been introduced recently.

Another thing to try is some of the homeopathic sleep remedies, such as Brauer's Calm and I think Rescue Remedy has a sleep one out now. I have had some help with that in the past. Maybe even pick up some Rescue Remedy for yourself.

I have also found that sometimes they do just go through that phase. DD2 about that age needed to be settled on a sling whilst I stood in the lounge room, then suddenly she was fine with being settled back in the bedroom in the dark.

Good luck