Turns out i was able to get onto the computer quicker than i thought

When i found out i was pregnant, i was only 8DPO, (i was charting my temperatures) and DH & I had only DTD once around ovulation, so was a total fluke really. But like you, i KNEW i was pregnant, i just felt different, and could tell. I'd never felt that way before after Ovulating or at any other time during my cycle. So I went to the docs, did a test there, and they referred me to my local hospital (why? i dont know) to get the blood tests and stuff done. The first HCG test i got done showed my levels were only 84! and 2 days later they were up around 200 and something. i also had a scan done on the same day i had the first blood test (turns out it was roughly 4w5d or so), and they couldn't see anything either, not even a sac, they just said the endometrial lining was nice and thick to support a pregnancy, but thats all they could say, so they got me to come back at a later date (i think a week later?) to also confirm that it wasnt an ectopic pregnancy.
Went back a week later (roughly 6w3d), and there was a tiny little sac there, but no heartbeat yet, so we waited another week, and lo and behold there was a tiny little foetal pole with a heartbeat racing along at 144bpm and that was at a gestational age of roughly 7w3d or so?

So just because theres nothing there, doesn't mean that you're not pregnant, like you said, it might just be too early to see anything yet!

And like i said before, as a general rule of thumb, as long as its not bright red blood, generally you're in the clear, brown blood is old, so not likely to be anything to do with bubs, it could even be that if you and DH have DTD that could be it? or even just a breakthrough bleed?