I don't have PCOS nor am I on metformin, but have been on/off/on birth control....
I didn't notice totally regulated periods right away, but they got a "little" more regular (normal) each month.
If this is your first time on birth control... Give it several months.... (it really does help to take it about the same time every day, and it is awesome to not have to worry "when" you should be starting...

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Don't worry, I am sure you will get it worked out.. Hope this helps