9 days late and showing negative results

Samare

Alright guys, I got the birth control Nexplanon put in November of 2016. I had it removed this past August on the 28th, I did not have a period the entire 2 years I was on the birth control. I had my first period after the removal on November 7th, it was regular and lasted 3 days. It is now December 16th, and my period is 9 days late. I have taken several pregnancy test and all were negative. Any answers or opinions?