I get the same exact thing. I am a medical assistant and really had a serious conversation with my doctor. My white count came back high and all my STD panels came back clean. this is what he advised me to do take it out! He said that the cervix is ment to be tightly closed only opening enough for tiny sperm to get in. When oxygen and other bacteria get into the hole where the IUD is inserted bacteria forms and you can even get sepsis. I dont want to take it out, but I am now considering it as Ive only had my IUD for about 6 mos. It also seems to get worst during the hotter months.
Fishy odor usually indicates Bacterial Vaginosis (BV), which is an infection. But I'm not sure why it would happen every month and be accompanied by sore breasts. That does sound a bit strange. Did your obgyn say anything about that?
I don't think IUD mirena give you fish odor. I think it's more Yeast infection. I have IUD for 4 1/2 years and never experience any fishy odor. I have only 1 day period, but as far as i known, there are no infection. Do you think you could get from STD?
good luck and take care