What causes irregularities in periods after delivery?

I gave birth for the second time eleven months ago and i only had my periods six or seven months after the delivery. at the beginning of this month i had my periods again and there was too much flow, a bit like after a delivery and that lasted for 5 to 6 days. The previous months before that, i was not bleeding that much and i could have only a few drops. What happened this month i don't know. And now two weeks after those periods were finished, am once again bleeding. not that much, just enough to wear a pad. Is this normal. Please advise.