What Causes Heavy And Prolonged Period?

Hi I am 24 years old, I had an early abortion about a year ago and have not been on birth control since. My period went back to normal the very next time, not too heavy at all and about 4-5 days long, every month. I just passed a blood clot about the size of a tennis ball/baseball and a weird shape....I am also having a period much heavier than normal, could this be a miscarriage and/or when should i see the doctor? My period has also been going on much longer than normal (almost 2 weeks) but has not been heavy like this all the time. I am very confused and scared.