Who took my baby!

Who took my sleepy baby and switched her with the monster I find in her bed at midnight? We had a few great nights where she slept for 5 hours, woke up to eat and then slept for 4 more hours! Night before last she woke up at 330am and didn't go back to sleep until 745am! Last night she went to sleep at 8pm, woke up to eat at midnight and wouldn't go back to sleep! At 230am I finally gave up and woke up Addam to try to get her to sleep. We finally just let her cry in her bed, she fell asleep after only a few minutes but seemed very restless the rest of the night. And again she is in the process of waking up from her less then hour nap. Hopefully we'll get some much needed sleep today!