I have pcos qnd just had a week long period that ended 7 days ago and now I just started again. Why is this happening?

PCOS. Pcos is notorious for causing irregular menstrual cycles, interfering with the desire to get pregnant and alters you fasting sugar levels much in the way as would a diabetic. Usually, birth control can help with regulating the menstraul cycles. You may also be placed on a medication called metformin in that will aid in preventing as well as treating diabetes.
PCOS. You are not ovulating so your having dysfunctional bleeding. Your body needs to ovulate to have a "normal" period. Mayo clinic has one of the best info sites on this syndrome. Google it and find their site.