How soon have you just known?

I read a few posts on baby center and it appears many women have just known they were pregnant within hours of concieving. What are some of your stories? We are TTC. I had sex every other day of the ovulation week according to glow. Yesterday (Saturday) was my last day of ovulation and my SO and I had sex Friday with 33% chance of conception. I took an OT each day and noticed that today the second line was very very faint (I'm assuming since the window week is enduring). Anyways, today I've felt some pretty moderate cramping and some string pains in my back along with diahhrea. My period is about 12 days away so hopefully it doesn't come and a hpt is a BFP! Have any of you just known? What's the soonest some Of your hpt has shown BFP after ovulation?