Chance of Pregnancy?

I'm currently 9 days late for my period - and it's been 5 weeks since my last one started - so I took the Clearblue home test. It came back negative, which was a huge relief! The only thing I'm worried about is why am I late? My period isn't exactly regular, but never this late. I haven't been more stressed than usual (there's always a little in life LOL) but is there still a chance I could be pregnant and the test came out wrong? Has anyone tested negative but was actually pregnant?