Bleeding is worth investigating if it soaks a pad or tampon every hour for several hours, needs double protection, lasts more than seven days, passes clots larger than a coin, or wakes you to change protection.
Fibroids, adenomyosis, polyps, thyroid problems and clotting disorders are all common causes, and most are treatable.
Heavy bleeding is the usual route to iron deficiency in women, so tiredness alongside it is a related symptom rather than a coincidence.
Bleeding that changes noticeably from your own normal is worth attention even if it would not strike anyone else as heavy.