Who's the cause?!

I've had the nexplanon for 1yr 1/2. Didnt get periods till 7 months later. Had irregular periods here and there but everythings been fine since 4 months ago maybe. Ive had unprotected sex about 4 x inbetween and have had pregnancy scares. Turns out its nothing because i would get my period. Now this month I'm 1 week late on my p. Ive had no pregnancy symptoms other than occasional cramping, lower back pain and sore breasts ALLL pms i get before my period. Should I be worried? Any of you have this problem with nexplanon??