My Aide Was Prescribed Bactrim For A Unitary Infection But

My aide was prescribed Bactrim for a unitary infection but the druggist substituted Sulfamethoxazole Tmp DS tablets which according to your web site is the Sulfa drug without Trimethoprim. The MD (at a an urgent care center) also prescribed phenazopyridine. Today she is feeling very weak with aching back (kidney area). Any ideas what to do?