Expired Nexplanon

I got my nexplanon three years ago in July. It expired this past july but I could not get an appointment with my OBGYN until late September to get a new implant. My period were always irregular and late on the nexplanon which was expected but after it expired they started being less late only by 5 days typically. I have been having unprotected sex which is not smart, I know. My period is now 15 days late I’m not sure if it’s just my body adjusting to my new home and new college, if i’m pregnant, or if i’m just simply stressed. I took a pregnancy test a week ago and another one yesterday both negative. Any suggestions?