Period for 15 Days

Grace • “Here’s to strong women - May we know them. May we be them. May we raise them.”
I'm 16 and I usually have irregular periods, as in, I'll go a month without a period and then a week or less with, two months without one, a week or less with. This is never happened before and I'm hoping it'll stop before I need to see a doctor. Does anyone know why this is happening?