late period?

OK I got my arm birth control on Tuesday and I was suppose to start Thursday and I didn't. I did have a blood test done to see if I was pregnant but it was negative. But I did have have sex with no condoms but it was only a few days before I got the birth control but couldn't they tell if I was pregnant even it was only a few days? Or does this birth control do this? Like I was on the pill before I got pregnant with my son and when I first got on it I still had my period that month. I'm just confused?

sperm can live up to 5days so u can get pregnant up to 5days after sex.....implantation occurs several days after conception & a bfp isnt obtained untill after implantation. you may want to test again to be sure. the implanon may be screwing up your cycle but since you had sex b4 insertion you could be pregnant.

Implanon? I haven't had a period since I got it in in april