Why do I keep getting negatives?😢

So this is my calendar for July 
I think their fertile window prediction was off because I didn't have egg white cm until the 26th. My boyfriend and I tried on the 27th and 29th. 
On the 1st of August I went to change my panty liner (I wear them around my period week so I don't wreck any of my underwear) and I had a little bit of brownish discharge on it (like old blood would look after your period) and that was it. Nothing else. So I thought maybe it was like and implantation sign (I know most people say pink but can it be brown?
My period comes every 25 days and should have started on the 3rd but it still hasn't arrived and I don't feel it coming at all like I normally do. Absence of all my regular symptoms.  So why do I keep getting negative tests? Is it too early to detect positive results or maybe I'm just not pregnant. Then where the heck is my period 😔😔😔

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