I got the Mirena a little over a month ago. I'm currently on day 28 of my period. It's been very light and sometimes just spotting. I know this is all normal. However, yesterday I had sex for the first time since insertion and during sex my flow got heavier and has remained that way. I think that makes sense, but I've read that if your flow becomes heavier after being light for a while, you should tell your doctor.