My daughters sleep patterns changed. ?

My 16 month old daughter goes to bed at 7 every night and has done since birth. I've never changed her bedtime routine,but she's suddenly decided to change it for me! She used to sleep 7 while 7/7.30 but for the past month,every single night she wakes up twice crying! If i ignore her she crys for about 45 mins then goes back to sleep,but if i go into her (i don't pick her up) she'll stop crying when she see's me but then as soon as i've popped her dummy back in and walk out she gets very destraught to the point of the rare occasion making herself vomit. Plus she's suddenly become an early riser waking every morning at 5.55 ready to get up. Any tips on how to get her to sleep straight through again? I really don't no where this has come from s there's no change in routine,no noise during night,no bright lights outside etc. I'm very tired!