Problem with IUD? (TMI)

So a few weeks ago I got the Mirena because I wanted something more long term than the Depo I had been on. o stopped the Depo in February and waited for my monthly visits from AF to get back to normal (didn't get them at all on Depo). My first monthly visit after getting the Mirena was about 3 days early I think. Its been well over a week now (typically my visit lasts 3-4 days) and it's not like normal. It's much darker and slower flowing than it usually is. normally I would've just attributed it to the change in birth control and moved on but I'm starting to get worried. I also had very severe cramping from the usual area all the way down my right thigh for the first day that it started. Should I go in to the doc or should I wait a little longer?