Bfns.. Convinced something isn't quite right

So we last dtd on 19th Feb.. And I've been testing since Monday.. All bfns
My question is..
When not charting when ttc checking cm/opks etc how long after last having intercourse would you test just to be sure and when would u class yourself out.. Even when AF is non exsistant. 
I have painful sore nipples, had bouts of nausea yesterday and today to extent where I have actually threw up..
I'm convinced I'm pregnant but nothing is suggesting I am via testing.. I'm hoping there's some explanation to this.. With last dtd being 19th it's been 19 days now if I had allegedly ovulated around that time.. But then on the other hand I may not have it could have been later... Question I'm basically asking is I tested this AM neg on cb.. Am I out.. 19 days is a long time right?