Period issues

My period is 8 days late. Usually seems to be a couple days irregular but has been getting better over time. I also have implanon in my arm that should have been removed I. 2013 (which I know already know I should go to the doctors) I have been faithful to my fiance of almost 6 years, so I'm sure it's not an std. But I have had cramps throughout the day, and just realized I have a dark brown bleeding type discharge with small clots. I have taken 2 pregnancy tests and they were negative. So I'm just wondering if any other females have had this issue and if so what was your outcome. I've looked online and all I see is pregnancy, old cervical tissue build up, or infection. Please help