Unusual menstruation

HI! Ive always had regular periods, even after having three kids. They've always started out with spotting then it gets heavy after two days then it dwindles again after four days This month is the first time ever that I started menstruating after 3 weeks, not 4. And it started out very heavy from the onset. I’ve had to empty the large cup about 10 times a day and get up to change it at night. It’s been three days now and I’m getting pretty sick of it. Any ideas why the sudden drastic change? I’m not taking any medications... Thanks :)

u need to visit your gp any increase in amount of bleeding or length of time thst your bleeding for needs investigating vaginal infections and numerous other things can cause a heavy flow