Is it normal for my mirena to still hurt 4 days after insertion?

It's normal. You can have cramps for a little while. I think mine really went away after two weeks. I usually only had them in the AM and they weren't too bad. After the 2 weeks there seemed to be about a minute in the AM every day that I would get a bad cramp, but that was it, just a short one. That went on for a few months.