it sounds like you don't want to get pregnant - sorry if I've misinterpreted.
So if you don't want to get pregnant, it would be better to get the contraception right, rather than worrying or trying to avoid conception - really women have got pregnant at all different times during the month, so the only way you can avoid getting preg is to mke sure you are protected- I'd go to the dr if I were you babe and get the pill or something.