Could I be pregnant?

Hi so I’m on the Nexplanon and have been since feb 2018. I haven’t had a period since June 2018 I believe. I don’t spot or bleed at all. I have normal vaginal discharge, nothing abnormal. But yesterday I started spotting. It’s continued into today. I had unprotected sex last Saturday. And many times before that. I’m just concerned because the bleeding is not normal for me and I read it could be implantation bleeding. I took a pregnancy test and it was negative. But could my birth control give me different symptoms? I’m just a lil concerned.