Nexplanon but worried

So I've had Nexplanon since December 8th and I've had the spotting for a month experience along with breaks and spotting for a couple of weeks. I stopped spotting about a week and a half ago after a month of it, and three days ago, I had more blood. it wasnt very much, but I noticed it and It was old blood and it lasted about two or three days. I had a little bit in my cm today but idk if it's enough to count as spotting. What I'm worried about is it happened about 11 days after I had sex. Im scared it was implantation bleeding. I'm on the very effective implant and we used a condom, so I know I'm super protected using both methods, but I've heard of lots of women who get pregnant while on birth control and while using condoms. Do you think this is just more random spotting? Or possibly implantation?