How can I slow what seems to be excessive vaginal bleeding?

Get seen, FIND cause. A common cause of menorrhagia (excessive bleeding) is 'hormone imbalance' but cancer must be ruled out with exam/pap smear/possible endometrial biopsy. An ultrasound can look for fibroid tumors of the uterus which can also contribute to excessive bleeding. If all tests are normal then a trial of hormones ('the pill') or an ablation may dramatically improve your bleeding.Hysterectomy is last resort.
Need more. This question is pretty vague. More information would be pretty important here as "excessive vaginal bleeding" can be anything from an unusually-heavy period to heaving bleeding while pregnant (a true emergency). Please give us more so we can help you better. At a minimum, we need to know if you are pregnant or not and if this is just heavy menstrual bleeding or something else.