What Causes Irregular And Missed Periods?

I am 21 years old/female. Sometimes I get my period every month for 7 days and times I go without it for 2-3 months. I don't really want to take any medication/birth control, is there anything I should be worried about?



Other info: I got my first period at 16. I have had 1 ovarian cyst at 18, and 3 kidney stones over the past 2 years.