What Causes Heavy Vaginal Bleeding And Abdominal Cramps?

Hello, i am a 20 year old female who has just recently been in a relationship that is sexual, up till this point my menstrual cycle has been pretty normal, untill a few months ago when its been weeks late. this month i menstrual cycle came on time and lasted it normal cycle 5 days. but a week later it started up again, the cramps are worse and the flow is heavy...is this a normal thing? i worry because i am anemic and am concerned this extra period will affect that.please help me