I am of 16 but it occur first time that i didn't got periods this feb. is it very serious issue or it will occur again this month?

Sometimes happens: In a woman with regular periods, some causes of a late period include: excessive weight loss or weight gain, increased exercising, emotional stress, having an illness, traveling, medicines (like birth control pills), hormonal imbalances, etc… in teens in their first two years of periods, missed or irregular periods are more common. Pregnancy is a common cause of a missed period, if having sex.