Yup EXACT same thing here. I was going insane and couldnt work out what was going on.
she just outgrew it, really. and i guess she isnt as good a sleeper as she was, she is at least sleeping for 3 hours at a stretch now, which i am really happy with.
I found that if i put her in bed with us then she would sleep better - leading me to believe it was all about separation anxiety. I think you just have to go with it. you cant force them to sleep - just be there to help them through this phase.
i know thats not much comfort, but it will get better