I'm 18 Years Old And I Have Problem Of Irregular

I'm 18 years old and I have problem of irregular periods from starting i.e., from my first menstrual. I get periods after 2 or 3 months gap. But this time after 3 months i got my periods and I'm bleeding for 15 days i also used medicine(trapic and bigspas) for five days after my 10th day to stop the bleeding but no use. So pls can anyone suggest me anything to stop the bleeding and the reason behind my problem