A BT can tell from the day AF is late, usually approx 4 weeks from LMP which is what the 40 weeks is based on. So 4 weeks pg is the day AF was due.

Chody, are you charting? It could be possible that you Oed late this month, in which case your LP might not be as long as you think it is. I had a 2 day discrepancy in my LP at the beginning of charting and FF told me that it was irregular so would be hard to become PG, I was pg in 3 months of actively TTC.

Alternatively, the brand of HPT you are using could be dodgy. I personally used First Response or Clear Blue for each of my pregnancies because they had the best reviews. I never had good experiences with fortel, like the control line never came up, and the Ebay ones were just too messy and flimsy.

Best of luck and