Definitely use pads at this stage Kerrie, until you find out exactly what is going on.

A HPT can still show a positive result even if you are having a m/c, and the reason is as Lucy said....that the PG hormone (HCG) remains in your system for a while and gradually declines until it returns to zero.

Yes, some people have had periods or some light bleeding around the time that AF would be due when they are PG and it is because the level of HCG has not risen enough yet to prevent some of the lining of the uterus shedding.