Hi, I Once Used The Nu-Isterate For About Two Years

Hi, I once used the Nu-Isterate for about two years and only stopped when I skipped 4 days of not being injected thus being a year since I went to the clinic for the injection. I have had irregular menstruation cycle's since then. Recently during November 2016 I had unprotected sex with the same man for a month and a half right but now I started ovulating in the month of December 2016 and probably after a couple of day's I slept with him, mind you I have done quite a number of pregnancy tests and they all came back negative. Could it be possible that I might be pregnant after our last in counter?