Periods Return After 1 Year. Normal?

Let me give some background so you know a little where I'm coming from. Before going on birth control, I always had irregular periods, usually 2 cycles a month. I went on the pill in late 2007, which successfully regulated my cycle. I was having concerns about effectiveness, and people were recommending Mirena. I got Mirena put in on October 31, 2009.

At first, my periods were about what's normal for me without hormonal BC. They gradually lightened up and were gone within a few months. About a year after I got it put in, they came back. And they've been getting heavier, again acting as if there's no hormonal BC.

I didn't notice the Mirena fall out or anything. (I haven't really been able to check the strings, though.) I can't find anything online about what I'm experiencing. Is it possible that I received a faulty one where the hormones didn't last as long as they should have? I also don't think it could have perforated the uterus because I'm not experiencing any unusual pains. Does anyone know if this is normal?