Thank you for submitting your question. It sounds like your menstruation is unusually heavy for you.
The amount of bleeding during menstruation usually depends on hormonal levels. The following are the usual reasons for heavy menstruation:
-use of hormonal contraception(e.g. depo provera shots, mirena IUD)
-recent stressful events
We usually recommend that women seek medical attention if they soak a pad in an hour. Your doctor may give you medications to stop the bleeding so you don't lose too much blood.
You should also know that a miscarriage or ectopic pregnancy can cause heavy bleeding and dark clots as well. If you think you may be pregnant, you should seek medical attention to rule out miscarriage/ectopic pregnancy.
I hope this answers your question.