WHERES MY PERIOD

im trying to convince myself im overreacting but for as long as ive had my period its been on the dot, a day early or a day late. today she was supposed to come but she didnt and im scared bc I recently just had sex (we did use a condom but im not on bc). ik I should wait a little longer u til I start actually freaking out but what should I do if I dont get it!!!! (im only 17)