I have had periods for over a year now, since adjusting after coming off the pill.
They are fairly random, but usually around or under 3 weeks.
Since Christmas, it has been reduced to spotting every 2-3 weeks, then a 32 day gap, then a period. I am not now sure what is a period and what isn't

I have been charting, but to be honest, it has been no help in predicting what is going to happen.