Is irregular periods a matter to be worried for a teenager?

Not necessarily. If : You've had periods for 2 years or more, it's time to woman up & have your first visit with a gynecologist, not just because you're not ovulating ( producing mature eggs that roll down the fallopian tubes), because it can take a while, but to learn breast-self exams, why daily Folic Acid supplements are important & to get your questions answered about safe sex, etc., without your mom in the room.

Maturity takes time: Irregular periods are caused when your body's signals for ovulation and menstruation get confused by hormonal imbalances that can be related to your thyroid (TSH), pituitary (LH/FSH/prolactin), ovaries (estrogen/progesterone). External factors can affect the hormones: malnutrition, stress, obesity, for example. Hormonal contraception can help to regulate your periods, but you might just need time.