Yep, I kinda had a similar situation to yours. After our frostie transfer, I got a BFP on a pee test, but had some bleeding commencing at 5 weeks. They did a series of quantitative HCG blood tests and they said it wasn't clear if I was really pg or if it was a chemical pg/early miscarriage. My numbers weren't doubling but they were increasing slowly. FS said we wouldn't be sure until embyro was big enough to see on an US at 7 weeks. Praise God, embie stuck and is now crawling around on the floor.