Why my period havent came yet ?

Missed period: It's not clear whether you've never had a period and are wondering about the delay with your first one or you've had periods before but the expected one failed to come. If you're concerned about your very first period, it's definitely warranted to see a doctor/pediatrician as it is not normal not to have period at your age. If you missed a period, do home pregnancy test to rule this one out first.

Need more info: Do you mean your period has not appeared ever, or it's late? There are many possibilities depending on what you mean. If you are just starting to have periods, then they can take a number of months to become regular.