What Causes Heavy Vaginal Bleeding After C-section?

I gave birth 4 and 1/2 months ago by C-section and started my first menstrual cycle 2 weeks ago. I began an oral contraceptive at the time. The first few days of the cycle is very heavy. I would soak through sanitary product and 1 hour. Since then it has decreased significantly. But I am still having some bleeding 2 weeks later. That meanest of the flow varies from day to day but it was nowhere near as heavy as the first few days. This evening the flow seems to have increased and I ve passed a few nickel sized clots. Is this something I should be concerned by or will my body regulate itself over the next few months?