What Could Cause Fluid Around Iud?

Today I went to the hospital for what I thought would be a simple uti or kidney infection, my general dr is out of the office or I would have just went to the office. My symptoms were pain in left abdomen, around back on that side...feeling a need to urinate and burning w urination, there were white blood cells in urine. But because of the pain location they also did an. Internal ultrasound to check ovary, I have had an mirenda iud for past 3week yrs...now there is fluid around the iud, and because of that they couldn't see the ovary. What could cause fluid around iud? What concerns should I have about my ovary. I am 32.....