Uti or yeast infection

I went to my OB monday with lower back pain thinking I may have a uti even though I had no other symptoms of having one. I get there and they get a urine sample and dip the little strip and said it looked ok but they'd send it off to the lab and give me the results Thursday at my regular appointment. I go Thursday and the nurse said my urine came back with a small infection, didn't say what kind though. Any ways they prescribed me antibiotics for a uti, ampacilin I think. So now for the past two days I've felt like I have a dang yeast infection. Could it have been the yeast infection that was picked up in the urine culture and not a uti? Should I go get some monistate(sp) and not take the antibiotics? So sorry it's super long I'm just confused.