Abnormal period

So I have been on the bar for 3 and a half years and am on my second one ( have been on my second one for about 6 months) and have only had a few short periods in that time, but I have randomly gotten my period and am on my 13th day with it and it’s getting heavier. My normal periods are usually about 2 days long so 13 days is really abnormal to me aswell as the heaviness of it. If I keep bleeding I will go to the doctor, I’m sure it’s fine but just wondering if anyone else has had similar happen or know why this could be happening?