I was doing very well at monitoring my menstrual cycle. I found it surprisingly helpful to be able to judge when I was likely to have a period; it meant I could prepare myself mentally for the crash. Recognising when I was ovulating was nice, too, because it let me pretend for the days when I'll need to know that for baby-making reasons and that made the periods easier to deal with because I could call it all a 'learning about my body' game.
My periods have tended to be erratic and I was surprised by how regular they were, as though I had been wrong all these years in thinking I was unpredictable and I just hadn't been paying attention. Only eventually I had a month when I didn't seem to ovulate, or at least, if I did ovulate I didn't recognise it. Now, being a bit on the lazy side, I was tending to fill in my calendar on my ovulation day rather than when menstruating but, because I failed to ovulate, I missed the previous period marking too. When the subsequent bleed began, it was early and then stopped and started again. The next month was the same - no apparent ovulation, period started early, stopped and then started again. I think I had three months like that. I haven't recognised an ovulation in that time and I'm now onto my fourth period (which may run smoothly or may be in its first step) and they aren't neatly regular.
It really does make things harder. It never occurred to me how much of a difference knowing when to expect a bleed would make, but it seems to be the diffeerence between waving and drowning.