Methotrexate shot

Hello everyone,
I found out I was pregnant on 9/1/10...then on 9/17 I started having heavy cramping and some red/brown bleeding/ The cramping and bleeding only lasted for 3 days and I called my doctor who sent me for 2 HCG's. They came back as abnormal (very low and only slowly rising.) I had a transvaginal ultrasound that showed nothing, however my Dr still was quite sure that it was an ectopic (because of my bleeding and due to my HCG numbers) so on Friday 9/24 he sent me for one dose of IM Methotrexate. It is now 6 days later and all I have been having for the past 3 days is some brown spotting...Is this normal? I have not had any cramping, no bright red bleeding. I am scared that the shot is not working?? I am so scared about having to have surgery or that my tube will burst. Does anyone have experience with this? What if my pregnancy was not ectopic? What would the methotrexate do to an intrauterine pregnancy??? This is such an agonizing waiting game...this is our first baby and I am so scared about what is going on! Any help or advice would be so appreciated!!!! Thank you!!