What Causes Delayed Periods While On Implanon?

I have been on the implanon for almost 2yrs and never missed a period since I started with it. I have been having intercourse a lot over the past 8 mths like twice a day and more some days. This is a huge difference from where I was 2 years ago. I have not had a period this month at all and last month it ended on the 13 and was very light. Is there a certain medications that can give you a negative??? I took two tests and both were negative. Do I just need to get a blood test done even if I got the negative results???