Any menstrual bleeding which goes beyond seven days would need attention. An heavy flow further deserves care as it can lead to anemia. With a history of missing period for two cycles and now a heavy flow points to some hormonal disorder. So blood work for thyroid, prolactin and FSH, LH would be needed. An ultrasound of the uterus and ovaries is also done to look for fibroid or polyp of uterus. Your primary care physician or the gynecologist will likely to prescribe you hormones to stop the bleeding.
Please feel free for your follow up questions.