UTI and antibiotic side affects.?

I have had a UTI for a week, and yesterday I went to the CVS Minute Clinic (I do not have insurance). I was prescribed SMZ/TMP 800-160 Tab as an antibiotic. After taking two doses of this, I have had extreme chills, then extreme sweating, a slightly high fever (100.4), and a TERRIBLE headache. I called the NA at the Minute Clinic back and she has changed my antibiotics, but I am worried that I have a kidney infection. She told me to take the new antibiotic and see if things are better within 3 days. I can't afford to go to a real doctors office, and I owe quite a bit to the ER... they probably won't even see me. Any suggestions/advice?