UTI SYMPTOMS HELP

Hey ladies I have a question soooo I was having UTI symptoms and kidney pain. I went to the doctor, well they gave me a 3 day course of antibiotics.. I called to let them know I was having the same symptoms only my kidney pain went away.. Well they called about a week later to tell me I had blood in my urine & I wanted for me to do another urinalysis so I did and the results came back the same.. She said I was negative for UTI but my results say I have MANY bacteria and still having microscopic blood in my urine.. I asked if I can get a different antibiotic and she said NO! She wants me to go in again.. I'm so confused.. I'm scared.. Is it even possible? Should I get a second opinion? Or should do another follow up there with the same doctor?