Are you breastfeeding DD? Even though you already got your period since you delivered, sometimes a woman can get her periods while breastfeeding, then if the baby starts nursing more frequently or for longer times (ie a growth spurt) the woman's period can come late because of it. Hormonal reasons.

Or it could just be a wierd late period.

But if you continue to have irregular periods, do see the doctor just in case you're having problems with your hormones. I don't want to scare you, but before I had any kids my periods became more and more irregular. Eventually I was diagnosed with Polycystic Ovarian Syndrome. My story had a happy ending because I was able to have children after Clomid therapy. But just keep an eye out and let your doctor know if this happens again.