Agree with the above. If your hormones are non-existent as far as triggering periods, any Sunday should be fine to start. Sometimes, we have that PMS shift, even when we don't bleed, and that *COULD* be an indicator, but basically, you're setting your body to a new schedule.

Depending on how deficient your hormones were prior to starting BCP, you might actually need to use a back up method for a full month before being "protected" by your BCP, which is generally only 95% effective anyway, even if you take it perfectly at the same time every single day with no exceptions in food, sleep, other meds, etc. Consistency in timing will aid your "adaption" to the medication, as well.

Good luck getting this to level out. Look into the previous posts here on Inositol and Vitex, too, as far as helping to level out your hormone levels more naturally.

EDITED TO ADD:

BCP can sometimes WORSEN your PCOS symptoms, depending on what form you're taking, where your hormone levels were before you started taking it, how your body reacts, etc., so I'd also recommend keeping a journal to help you figure out if what you're taking is good for you personally... Remember that there are literally hundreds, if not thousands, of birth controls, one of which might be far better or worse for your individual body.