What Causes Delayed Period,nausea And Mood Swings While On Implanon?

I have had the Implanon for 15 months now. It has been messing with my menstrual cycle since day one. My periods are unpredictable but they are never more than 8 weeks apart. I have not had my period for 10.5 weeks now and would like to know if there is a possibility that I might be pregnant. I have taken two at home pregnancy tests and they have both been negative. However, I have had heartburn/nausea for the past month or so and I get headaches, mood swings, and I find myself to be hungry a lot lately. I don't have tender breasts and I haven't gained more than two pounds though.
So, might I be pregnant? Can a blood test determine if I'm pregnant?