What Causes Chills And Fever After Taking Bactrim For UTI?

I have a UTI and was prescribed Bactrim and was given sulfameth/trimethoprim. I have had a UTI in the past and was prescribed Macrobid. I had an allergic reaction to Macrobid. Does Bactrim or the prescribed substitute have some of the same ingredients as Macrobid. A symptom of my allergic reaction was chills & fever. I am currently experiencing chills and want to know if that is from the UTI or a reaction to the Bactrim.