Missing Aunt Flo

Has your period always been on track and then when your expecting it to come on it doesn't? My period has been pretty regular since having my baby last year and even before that. But I'm due for my period today and she's no where in site. Though I have all the feelings like she's coming on, there's nothing. I don't want to get my hopes up because we want another baby, would be are last though. So I'm guessing my question would be have your period not come on the day it's suppose to and you later find out you're pregnant?