What Does Black Specks In Urine Indicate?

I have been having black specks in my pee lately and there not hard but I m wondering what is causing it. I m 22 and female and it started about a few days ago. I do have pain right above my pants line under my belly button. But I went to the ER for that pain and they ran a blood test and pee test also a ultrasound and didn t find anything. Except cysts I knew I already had on both my ovaries.