Hello. Even a single drop of blood is not normal in urine. But there is nothing to worry. Kindly visit a urologist. He may advice a urine routine examination, xray to look for stones in ureter bladder and kidney. This pain in back suggest a stone probably in lower end of kidney. He may also advice an ultrasound which is excellent modality of investigation for these symptoms. Bleeding occurs commonly when the stone moves( if that s the case) that means it can come out without treatment. Just have to drink clean more often. But sometimes there are some other pathologies in the kidney which can cause these symptoms. You may also be advised full blood count and renal function tests. These investigations and examination by doctor are mandatory for a prompt diagnosis. Anyway you must visit a urologist/nephrologist. Hope that answer the question. Thanks