Pregnant?

St
Im on the implant and my boyfriend has ejacualted in me multiple times, but due to my implant I haven't had my period since July! (Haven't been sexually active until August)  It's September now. I know it's unlikely that I'm pregnant, but how could I tell if I was? Would the pregnancy test still be correct even if I'm using the implant? What are some symptoms I should look out for?