Why My Period Is Late With Stomach Cramps And Tiredness?

Hi , Im 15 years old . Its around the time for my period to come on , But i havent seen it yet . Its usually on the sametime my mom's is on . But now her's done went off so i know its time for mine . I had sex for the first time in june (orjuly) but i think june . and he used a condom , and he didnt ejaculate either . Plus i been having these really bad cramps , and sleeping alot . And im kind of worried and scared .