Ugh! Ok so I’m 13 days late and took a test 3 days ago

Ok so here’s the back story. I’m on the nexplanon, have been for nearly 3 years. I can’t find my card but I know I got it put in at my ob check up after my second and she turns 3 the third. Anyways me and the hubby have been in a slump and really only had sex one time at the end of last month right after my period ended. We had sex 3 times this month. 18th 19th 20th and I swear my period is coming but it got to the end of the month and still nothing. I took a test the 27 around 4pm and got a negative though. So what the heck is going on? I’ve had my period regularly for over a year. TIA