Suggest Medicine For Missed Periods After Intercourse

I have sex my gf on 2 feb and his period got last time 21 january and the peroid come on that month 21 feb but period not come on 21 feb and today is 3 march ii cheack two time by pregnency test but result is negative. Now i have what doing for come period can i take unwanted tablet in this condition. Plz plz tell me