The use of this medication

About 15 yrs ago, after drinking some pills for an infection in the urine, I developed a rash and the Doctor informed me I was allergic to Sulfa. Yesterday I had to see a Doctor because I had infection in the urine and although I told him I was allergic to sulfa, he prescribed this medication. I already started taking them but I am worried. Please advise..........Thanks very much for your attention