Is that normal?!

Ok so I got the arm Inplant (birth control) about a week ago. I was supposed to have my period 5 days ago and I never got it. The doctor said in about 3 months I wouldn't have a period anymore but it's only been a week since I've had it!! The day before I got the arm implant I had unprotected sex (I know, stupid). So if I was pregnant it wouldn't have showed up on the test they made me take the next day. The implant starts being affective 2 weeks after getting it. I also had sex the few days after I got the implant.  I don't know what to do. Should I be worried? Or is that normal!