11 days late...

I'm now 11 days late for my period which was meant to start on the 20th. Last period was Christmas Day! I took a pregnancy test 3 days ago that was negative, I'm so confused! Wouldn't say I have symptoms as such, breasts are slightly tender and feeling a lot tired than usually but that's natural before a period!
Anyone gone though similar and been positive? If not, what happened? Please ease my mind😊