Paragaurd help!

So I'm 4 months postpartum. I got the paraugurd iud inserted on June 20th and got ( I guess you can say) a period right that day? It lasted the normal 7 days like I would usually get. Any way I haven't gotten a period ever since? I'm kind of confused bc my doctor said i would probably get a heavier period on iud. Is it because I exclusively breastfeed? But becore the iud I had gotten my first period? Is it because now I have more milk? Help!! I took a pregnancy test and it was negative. And I had gone a month later July 22 to get the iud checked. She said it was in place and I wasn't pregnant. But still noooo period!