Around 2010 my nearly always exactly 28 day cycle shortened to 19 to 21 days. I mentioned it at my annual exam in 2011 and my gynecologist at the time suggested I watch it a few months and if it continued to be short we should look for a problem. I was pregnant a few months later, delivered in 2012, and normal, 28 day periods returned at the end of 2012. In 2013 I experienced very heavy, clotty and prolonged periods all summer, became anemic, took iron, returned to normal for the winter. In 2014 again had heavy, clotty periods and prolonged spotting for the summer, anemia again, skipped periods for 3 months in the fall then returned to normal again for the winter. 2015, cycle began lengthening to 5-6 weeks for a few cycles, then missed 4 months. Tested FSH over 100, then had a period. Started cyclical HRT at the end of 2015. I'm not sure if I would have had more periods or not. The natural periods I had in 2015 were much lighter, like pantiliners the whole time and maybe 1 or 2 tampons) and only lasted a few days.