3 weeks long 😰😰

i've had my period for about 3 weeks now, at first it started out normal and i thought it had ended normally, but the next day i noticed some spotting. i thought it was just my period finishing it but it continued for a few days which is weird. then my period started up again really heavy, ended a few days ago and now im back to spotting? 😨😨 im going to the doctor on sunday but does anyone know what it could be?😞