When does Implanon become effective?

I got the Implanon birth control implant put in on April 26 (4 days into my period) and had sex without a condom exactly 2 weeks after it was put it. Could I be pregnant??? I am supposed to start my next period around the 20th of May and so far i haven't had my usual period symptom besides cramping. I have been really tired lately and have had headaches and backaches and stomach pain. Also, since i just got the implant in will my periods be not normal? Ive heard implanon becomes effective 7 days after insertion, so i should be good right? I just want to put my mind at ease.