What Could Blood In Urine With Severe Back Pain In Spite Of Taking Antibiotics Indicate?

Hi I am a 26 yr old female. Fairly healthy and stay active. Last week (sunday) I noticed blood in my urine that was pretty distinct. Everytime I urinated with no other uti symptoms. Monday I went to the doctor and she tested my urine and said I had a high white blood cell count. Most likely a uti. She prescribed me bactrim for 3 days while we waited for the culture. By the end of the 3 days I had hardly any blood and was feeling better. The culture came back not a clean catch. After 24 hrs of not being on antibiotics the blood in urine was back with horrible back pain on my right side. Friday she prescribed me 7 day course of Macrobid. After 4 days of being on the antibiotics I have on and off spotting in my urine depending on how active I am. Occasionally back ache. I still have 2 days left of my antibiotics. If I still have blood in urine by end of antibiotics should I ask for bloodwork and ultrasound or another week of antibiotics. Im nervous to get off antibiotics for that the infection hasnt cleared up. Does this sound more like a kidney infection or something more serious?