Pos then neg?

Hi all.
My af isn't due to arrive until tues.  being highly impatient I tested on wed and got the faint pos in the pic.  Then all day yesterday I kept getting negatives.  I still have Preggo symptoms.  I used the same brand of tests and peed at different times during the day and couldn't even get anything faint to show.
So my questions are
1.  Has anyone had something like this happen where you tested way early got a faint pos followed by a neg (or several I used up my tests yesterday willing my pos to come back) yet ended up pregnant?
2.  Is it possible by testing so early that on that that one day my hcg was just enough to catch it and does it fluxuate early early on that maybe yesterday was still just to early?
I am probably looking at a chemical but I'm looking for some hope...or some real honesty. It's just weird. I woke up today stil with my heartburn (which I only ever get when Preggo) and tender boobs again...