Quoting PeanutButter*HerbalifeLad:" do I always start my period when I'm not home? The past 6 times I've started my period I've been at MILs ... [snip!] ... I have pocs so it's not like I know when I'm going to start bleeding.sometimes I go months without one Mother Nature hates me"
What helped me to know when I was going to get it (I have PCOS as well) was taking my temperature and noting changes in cervical fluid and charting them. It told me around when I ovulated and when to expect my period. Of course, if you didn't ovulate and have breakthrough bleeding that's a different story, but it helps most of the time.