bad cramps, no period, never had sex

all week i've had such bad cramps and i keep panicking my period has started in class but i go to the loo and no period, today is my new period day and it hasn't come. i researched cramps but no period and many people said it's pregnancy signs, i've never had sex, may have done some oral but never sex. i know it's impossible to be pregnant but i'm freaking out!