after effects?

I got my IUD on March 10th. I've just been spotting since then, which is fine, but it has no pattern. I'll spot for a week or so and then all of a sudden stop for a day or 2 and then, boom! Here we go again. My doctor told me I'd get a super heavy period about 2 weeks after the insertion and then things would level out but neither are happening?? Should I be worried or should I just give it some more time?