Sex and Mirena IUD

Okay so I got my Mirena put in May 11th and I didn't have my period till the 13th it lasted for a week and a half and I waited a couple of days to make sure I was actually off my period and me and my bf had sex and I came back on my period which lasted 4 days and then I was off again and this time I waited a whole week to have sex with my bf and after we had sex I came back on my period again... Its almost as if every time I have sex I come back on my period this didn't start happening till after I got this IUD put in. Has this happened to anyone else?