Someone check my math?!

A. ❤️
Does this make sense to anyone or do I have some numbers off? 
8/5 was last AF
Small brown spot on 8/16 (??)
8/25 was O day according to glow
AF was due 9/8
BFN 9/4 and 9/12
Implantation can occur something like 6-12 days after O which would at the far end be 9/6
HCG doubles ever 48-36 hours. Again going with the far end I get:
1 at 9/6
2 at 9/9
4 at 9/12
8 at 9/15
16 at 9/18
32 at 9/21
FRER can detect HCG at 25 so that means I wouldn't hey a BFP till after the 18th?!
I'm a full week late now and too hopeful. No PMS or anything. Very light cramps here and there. Lots of CM since O.