What could be the possible reason for sometimes having periods twice a month?is it considered as an irregular one?its link with pcod?

Not ovulating : In conditions where you don't ovulate (such as PCOS) the uterine lining builds up very thick and eventually can break down and then you bleed. This is not a true period. It can lead to multiple bleeding events per month. If you take a 10 day course of progesterone each month you will have a full menses and, since this is not contraception, you can still get pregnant.