What Does Missed Period And Only Slight Spotting Indicate?

I've been taking loseasonique for 6 months now. I was suppose to have my scheduled period, but I have taken all the pills and still no period. I had very slight spotting for about an hour one day, that is all. I have taken a pregnancy test and it was negative. Could it be because of stress or something else even though it is suppose to be controlled by the pills I take that week? Or could I be pregnant even though the test was negative?