Nexplanon & sex..

So I got on Nexplanon 2 weeks ago (October 19) & my boyfriend has been very eager to have sex since. Tonight he finished in me but I’m a bit concerned bc I don’t know if the Nexplanon will have its “full affect” since the doctor did tell me to wait a while before having sex again.

I do know it can stop my periods & technically I was supposed to be in the middle of my period week today so I’m not too worried, but I don’t know. Should the Nexplanon already help me not get pregnant or should I take action?

(Sorry if any/all of this is very repeated, just a bit worried)