Simon not sleeping

Simon has had trouble falling asleep a lot lately. It's all a blur, so is lately a week or two? a month? Your guess is as good as mine. I just know that on many nights we'll hear him talking and singing until 10 or 11pm. Some nights he cries and one of us has to go in and rock him to sleep. One night I put him to sleep three times. We don't know why. Just a phase.