Sarah.. I'm not a nurse but...
Like you I had quite a bit of brown spotting from about 3 days before testing (it continued until the day after i tested!) My clinic told me that brown blood was old blood and not to worry too much but to call immiediately if it became red. I got a BFP on 03/08 and straight away my clinic put me onto gestone jabs to up my progesterone levels which seemed to help. So... try not to worry too much if you can!! I know it's hard!! I think it can be quite common at this stage of the the 2ww!!
Lots of luck and take care,
Callie xxxx