I pill is an emergency contraceptive pill (ECP). Like all ECP it needs to be taken ASAP after unprotected sex and within 72 hours. Earlier the better. Since you have not specified when the unprotected sex happened, if it is less than 72 hours ago, you may take it. But if more days have passed, its futile to take it.
Next Steps
Better do a urine
pregnancy test, as one month has passed since the last menses, If positive you are
pregnant. if not positive, you are not pregnant. Seek help of a gynecologist if the need be for future.
Health Tips
ECP are high dose pills and they can cause alteration in the menses cycle. So if you are having very infrequent sex, you may use it. But if you are having unprotected sex more than twice a month, it is better to be on regular OCPills.