What Causes Prolonged Periods With Bad Odor?

hi, I had a mirena coil fitted 6months ago I'm twenty three years of age. this is the second one I've had. I didn't have periods before and didn't expect to keep having them this time. they normally last a week or so, starting at the beginning of the month. but this month has lasted twenty one days and has a very awful smell, this has never happened before.