Beyond confused... need some advice.

My period is 3 days late today. I took a First Response early detection this morning using my FMU and it was positive... as in 2 solid lines. Then I took a Clear Blue digital and it said "not pregnant". I had it as an extra in my bag & took it for fun. But now I am super confused. I am pregnant or not? I know only blood test can tell 100% for sure. What could this mean now? I had a miscarriage Aug. 15th... could it be that the FRT was still detecting HCG? Ughhhhhh....