The morning after pill aka (plan b) can effect your cycle dramaticly!!! A bleed every two weeks is not normal. It means you have a hormonal balance and will probably mean you are getting low on iron. Go and see a doctor. They will probably put you on the pill for a couple of months to get your system stabilised. None of these bleeds you have will be a "proper" period. A period usually comes after the egg has been released and not fertilised. Two weeks is not longer enough for this to happen, and therefore it is your hormones going a bit haywire causing the bleeding.