Hi, My Period Is Very Irregular. It Usually Happens Once

Hi, my period is very irregular. It usually happens once or twice a month, but comes at random times. i got off my period last week, which lasted 12 days. i thought that was pretty odd because 12 days is a long time and that has never happened before, and it just came back today, which is also odd because my last period only ended 9 days ago. What is the cause of this? Should I see a doctor?