What Causes Stoppage In Periods?

I have not had my period last month but was spotting for 2 days when my period was "suppose" to arrive. I took a pregnancy test (First Response) 5 days ago and it read I was "Negative". So, I waited till yesterday and took another pregnancy test (Clear Blue DIGITAL) and that also read "Negative". I was looking online lastnight asking people if they have had a similar story and sure enough lots of people had some quite interesting ones. Like, their tests came out all "Negative" cause of their low 'ph' level and 5 months later they find out they are 5 months pregnant. Also, someone mentioned that it could be cancerous or a miscarriage. I really hope its not any of those. All I hope is that I am. My fiance and I have been very very sexually active...before and after iI spotted for 2 days. So today, I went to a walk-in Clinic afterwork and told the doctor my story...I felt like he wasnt even interested and just wanted to send me on my way. He made me urine in a cup, so I could take another pregnancy test. So that also came back "Negative" and then he sent me to go get bloodwork done ( cause I asked him if thats okay to do that just to make sure) so I wont hear back in 3 days. Can you help me in this situation? what could it be? please let me know. Thanks :)