A bit worried... for no reason?

I’m on Nexplanon and have been since December of 2016. I haven’t had a period since September of 2017 (wasn’t pregnant, just my birth control). I hadn’t been sexually active since August of 2017...until about three weeks ago. We used condoms, but I don’t think he changed right away when he came. He waited a few minutes before he would. I know even still it’s a low chance considering how effective my birth control is, but it still worries me a bit. Can I get your thoughts?