Implantation

Hello everyone! I need you opinions. This morning I woke up to a decent amount of dried blood in my underwear. I have been on a 28 day cycle combination pill for almost two years now. Today was the last day before my placebo pill. (February 26th) I had unprotected sex February 3. I have never experienced this bleeding before my period, and am concerned it is implantation bleeding. I have never missed a pill. I took a test, getting a negative result. But I am worried that it was inaccurate due to the fact that it is still a day or two before my missed period. Thoughts?