Copper IUD

I've had the copper IUD for almost a month now and I've been bleeding for about 16 consecutive days. At first it was so heavy and the cramps were so bad that I couldn't get out of bed (and I have a very high pain threshold!) It's calmed down now with no cramps and very light bleeding but it doesn't seem to be stopping. I've got my month checkup on Monday but just wondered if anyone else had experienced bleeding for this long?