Advice please

I'm 19 days late on my period all tests have come up negative. Could you be pregnant and only getting negatives or I'm assuming I must of ovulated late as had all the ovulation symptoms on the 7th of this month last period was the 28th June I have a 29 day cycle that usually is like clockwork I've never been this late bar with previous pregnancies. My question is do I wait until the 21st to test again as keep getting negatives. And if it does come up positive(I know jumping ahead a bit) when do you count pregnancy from would it still be the first day of my last period. Sorry I don't want to sound clueless