My 21 month old has decided to stop sleeping. She's been a great sleeper since about 5 months when we did gentle sleep training, but in the past 2 weeks she won't nap, or go down at night. She screams and cries for over 30 minutes at a time without letting up, until eventually one of us goes in and attempts to soothe her (which sometimes works, sometimes doesn't). She literally has been up until 9:00/10:00pm this week, sobbing. We've tried changing naps, keeping naps the same, doing the same routine, trying a different routine, we even took off the front rail of the crib and nothing is working. Any suggestions?