Why else would I be late?!?!

Danielle
Hello, my name is Danielle and I am new to using this app I am a mother of two, my daughter Peyton will be 1 on Tuesday and my Son MichAel will be 5 in May. I was looking for insight as too any other reason my period could be late aside from being pregnant again. I was due for my period on the 22 and there are still no signs of it.... Since giving birth a year my period has been like clock work, so I took a pregnancy test yesterday and it came back negative. Soooo I was wondering since I've never been this off before if anyone else out there has experienced something like this! I