How long is too long

I had my Mirena IUD taken out in early December last year 5 months ago, last month I got my first period in years which lasted 15 days of mostly medium to light bleeding. 16 days later I started this period and I am currently on day 18 of HEAVY bleeding. At what point should I be concerned enough to contact a doctor?? I know it is normal for the body to go through some irregularity after a hormonal contraception change but this seems excessive and unhealthy.