so ive been haveing unprotected sex for about three weeks or four weeks now i should have started my period about a week ago and i havent. but i also just got a depo shot 2 weeks ago. i have taken 2 pregnancy test and both have showed up negative. i need help i dont know what is going on because i have also had a little bit of a dark brown discharge off and on for a week & all it is is spotting very lightly. almost just everytime i use the restroom. what is going on ?