Dark Brown blood and a lighter period?????

Stephanie
Hi ladies. So this is my fourth period with my copper IUD. 
It's exceptionally light and very dark in colour. No cramps. Which is odd, as my past periods with the IUD have been heavy as hell with all the cramps of Satan. 
Is this normal? 
Also, this is totally naaaasty, but I got some real fleshy, membrane-like discharge with my first couple of periods. Anyone else get this?