Should I go to ER?

My lower back has hurt for 4 weeks now. I went to dr a few days ago for something else, and they tested my urine. Said I had a count of 80,000 for bacteria, prescribed bactrim for uti.

Past few nights back pain has woken me up and I cannot get comfortable. Tonight its at its worse. Having chills and nausea too. I'm afraid that its my kidneys.