Hi Starr,

Unfortunately, some HPT's DO give false positives. There is one brand that some of the girls have reported this happening with but I can't recall the name of the brand (sorry). The BT would be the most accurate way of telling if you are PG or not. Considering you still haven't gotten AF, I would go back to your doc and talk to them about it.
In regards to knowing if you are fertile or not, there are ways of knowing such as watching your body's production of CM which increases around ovulation, monitoring your temp (you need to be regularly charting to notice the difference) and of course there is also OPK's.
I hope you get some answers soon hon.

MG