Really heavy flow? bad cramps?

Just looking for anyone else’s two sense. Does anyone know why some periods are worse than others? I have been off birth control for almost 5 years now. My cycles are usually very regular about 24-25 days, periods are medium flow and about 4-5 days long, minimal cramps. Every once in awhile though I have a shorter cycle (sometimes only 17 days) that always starts with a sore throat, migraine feeling headache and almost debilitating cramping. I call these my “bad periods” super heavy flow and can last up to 8 days. I guess I’m just wondering if anyone knows why this happens and/ or can relate?