lmp with brown spotting

ok...here's my issue. My girlfriend and I are trying to conceive and i need some advice from you guys. My lmp was 12/11/07 and i have a 35 day cycle. I'm having symptoms on and off. I've had a little bit of nausea but no vomitting and my breast haven't really gotten bigger. now according to my calculations I would be 7 weeks pregnant. Begining on 2/2/08 I began spotting and got a little scared. I've taken 4 pg test between 1/11/08 and 1/21/08...I just gave up testing after that because it's too stressful. I usually get af every month but i havent seen her last month and now it's approaching another cycle. i should expect her in 3 day...but instead of af i received spotting for a week. It's not heavy enough for a tampon and the color ranges from pink...to brown. now it feels like i have a knot on the left side of my stomach...but i haven't been experiencing much cramping. why would I get neg test results if i'm indeed pg. i have a dr appt on tues 2/12/08 so hopefully the blood test can give me a definete answer. it's killing me to wait...i had an appt on 1/31/08 but it was cxl...causing me to wait another 2 weeks to get an answer...but i havent taken another hpt because i fear recieving another neg hpt. Has anyone recvd a neg hpt to later find out that they were indeed pg? If so, how far were you when you found out...and how many neg test did you get b 4 you got a positive? Please help...i'm scared that my baby may be in danger but until i get a pos result...i dont know if there's a baby really in there. Is there anyone out there that can relate?