Most unlikely you are pregnant. The Mirena IUS is one of the safest forms of contraception there is. One of the benefits of Mirena is that for most women periods become lighter and often stop completely. This is what has happened in your case I imagine.
If you are peeing more than normal or its stinging when you pee you could have a urine infection and should have a sample of urine tested by your doctor. I can’t think why urinary problems would be connected to your Mirena, its nowhere near your bladder.