bad luck? variance? rigged rng?

[sosorry]

I keep getting sucked out by 1 card straights or flushes, after I'm all-in or calling someone who's all-in (.05/.10c BB 10$ max). I have them beat but then they catch runner runner runner runner and beat me because they hold one of the cards that gives them a straight or flush.

My question is, does anyone know the odds for how often 4 cards on the board give someone a 1 card straight or flush?