Today has made it eight days that I’m menstruating and I know it will continue because I’m still bleeding so much. May I fast tomorrow even if I’m still bleeding?
You need to make sure that it is menses and not non-menstrual vaginal bleeding. If it is menses it is prohibited to fast. According to Shaikh ibn Al-Uthaymeen you wait until fifteen days have passed then consider the blood non-menstrual vaginal bleeding (استحاضة, Istihadhah.)