I'm not sure if i am pregnant or if something serious is going on.?

it was around the beginning of this month that i started wondering if i was pregnant. my boobs became really sore, so it crossed my mind but i just looked over it. then i was watching american idol and cried when someone got eliminated, when i told my bf he mentioned something about me being pregnant and that's when i really started worrying. i have waken up with terrible heart burn. i am dizzy almost every morning. i went and got a test it was negative but it was also two weeks before my period. as of right now my period is in three days. i have spotted twice, but now i am bleeding a really thick dark red almost brown blood. it isn't a lot its just off and on through out the day. my lower back is very sore and i feel like i'm having terrible cramps. i'm emotional as can be and weird cravings.. like milk? i hate milk. i have never spotted before in my life, my boobs never hurt..only time that happened was when they were growing back in middle school. i'm scared and i need some really good answers please. i have never had cramps this bad, back never hurts like this when i'm on my period.