What Causes Delay In Periods?

I recently found out i have pcos - I'm a slim young lady, and quite healthy too.. However, all results including all my levels, blood, sugar etc are fine, however my progestrone levels are quite low. I was on the Pill (Yasmin) for 3/4 years and stopped taking it a week prior my wedding.



I tend to get my periods every month, but I've noticed my pattern to be a bit weird. Two months my periods are fine, and then the 3rd month i get them 10-14 days late. Y is that so?