Confused!

I usually have regular periods I'm on the pill & when I'm on my last week I usually start within that week well I'm now 16 days late I've had some pains where my ovaries are I've had a cyst before. Could that make me not start my period? Could it be something else? I only had those pains like two days & it was on one side one day & the other side the next I haven't had the pains in a week.