Black specs in urine

So this is probably TMI I know. But, I have been having black specs in my pee for the past few days. They float on top of the water. At first I didn't think anything of it but it's happened two more times. I think it could be kidney stones? I have had a pain in my back on the left side if I'm on my feet to long. I'm 28 weeks along! Thanks in advance! I'm calling in the morning just to make sure but I'm kinda starting to really wonder what it could be.