I don't know...you may need to give it a bit more time. But f/u with the doc before the weekend.
I had an IUD once for about six months...didn't bleed between cycles, but when I did it was like a faucet was turned on. I would go through 2 or 3 pads an hour. My ob kept telling me it would get better after about 2-3 months so I waited...then I just couldn't take it anymore and had it out. Would have loved it had it worked, though.
Just think it may have something to do with my anatomy -- maybe yours too?