welcome to hcm
thanks for the query
first confirm that when is your monthly expected time of period.if its not the time then it may be due to some hormonal
contraceptives taken by you
if you have taken contraceptive after first intercourse then there is chance of getting irregularity in period.
or it may be trauma to the private parts
if still its not the case then consult your doctor about it. now you can take good amount of water.