Periods

I’m a 17 year old girl, and I have a question. I have the IUD implant, I’ve been sexually active before, not currently. Anyways, my cycle ended today, but you see, I was on my period for 13 days. Should I seek a doctor, should I just let it go, should I be concerned? Pls help I’m confused.

And mind you my periods are usually fairly normal lasting about 8 days, and they come every 28 days, so this is all of a sudden.