I Just Got On The Depo-Provera Shot And I Am

I just got on the Depo-Provera shot and I am a day late on my period. I've been on the depo for about a week now, could it end my period this early? I've also had a brown discharge and this morning a couple of red spots. I've taken two at home pregnancy test and they came back negative. Is it too early to test? Could I have a false negative.