I Stopped Taking My Birth Control Shot (Depo Provera), I

I stopped taking my birth control shot (Depo Provera), I was due to get another one on the 3rd of February of 2016 and decided not to get it. I haven't been feeling the greatest, so I've taken a few pregnancy tests and they all come back negative. So my question, I guess, is, is there a chance of pregnancy and me not know? Or could there be something else wrong? I have not gotten since the time I started that birth control.