Diagnosed with bladder infection, but kidney pain keeps getting worse. Normal?

3 days ago I went to the doctor for having kidney/bladder infection-like symptoms (painful/frequent urination, fever, nausea, back pain). They said that I had a bladder infection and prescribed me sulfameth. Since then, my back pain has gotten severely more painful, making it impossible to sleep, and even painful to move at all. At this point the back pain is only on one side, but is getting to be intolerable. Does anyone know what else could be going on, or if I should go back to the doctor? Thank youu!