BFN and losing my mind.

How has this not happened yet?! My sister got pregnant on the very first try! People get pregnant on accident ALL the time! People get pregnant at all different points in their cycle! How is it that we're having sex every other day, double timing during ovulation, AND using Preseed every time, and.... Nothing?! I'm so frustrated and I can't let my hubby see I'm crying because he doesn't get it. He just says, "It'll happen. Don't get so crazy over it." They don't get how this feels.