It doesn't sound at all like a miscarriage. Are you on any birth control at all ? Seems you have an irregularity in your menstrual cycle. Different things affect this such as age, menopause, birth control, certain medications, stress, and many other things. But in my opinion it definetely doesn't sound like a miscarriage. I would consult with my obstetrician though about the problem at hand.
Your age shows 30 years. It is possible you are having a thyroid problem. Being hypo thyroid can result in heavy and prolonged periods. Have you had that checked? Dysfunctional bleeding can be a hormonal issue as well.
Bleeding for a month after a miscarriage (if it is one) and left untreated is highly dangerous for infection and anemia. If it is a miscarriage and it has not come away properly can lead to prolonged bleeding and the chances of uterine infection is high.
I strongly suggest you go to a doctor as soon as possible and explain what is going on.