Kidney Infection-antibotics would make pain worse?

I was diagnosed with a bad UTI/kidney infection yesterday. I was told by my doctor that I had a bad infection/ alot of blood/ keystones in my urine. He gave me shot of something in my hip to "kick start" my oral meds. I started them yesterday afternoon (as directed). Today I'm more nauseous than yesterday and my kidneys/back hurt ALOT more than they have been. Is that normal??? They said if I didn't feel better by tomorrow at lunch to call back and I needed to come back in; but I don't understand why I would be feeling worse..... any suggestions??