What Causes Heavy Menstrual Bleeding After A Gap Of Few Months?

I stopped having my period almost 24 months ago after 3 years of on and off again periods. I thought I was well beyond menopause and could not get pregnant. I was shocked to suddenly have a period or miscarriage a few days ago. I started bleeding like a period of the old days. Lots of bleeding. I thought a I saw tadpole looking excrement in my pee and was sure it was a miscarriage. I am just not sure what happened. Any ideas.