Late period

Hey girls. I know this sounds like a ridiculous question but I'm wondering if this has happened to anyone else? I've been taking the same birth control, very faithfully I must add, since after I gave birth to my son 2 years ago. And I'm now 18 days late for my period. This has never happened to me in all my years of having my period. The only time it did happen was when I was pregnant. I took a home pregnancy test and went to the doctor and it was negative both times. So basically I'm just wondering if any other girls out there have experienced this before? I'm getting worried.