This condition is called menorrhagia. Normally the period stays for 3-7 days and comes in 21 to 35 days. However sometimes normal periods can be irregular. The causes of menorrhagia could be due to bleeding disorders, vitamin K deficiency, excess usage of aspirin, hormonal imbalance, stress, fibroids, recent intra uterine devices (like copper-T)etc. So I will like to advise for internal examination with gynecologist and take opinion.
I hope it helps. Take care and regards.