A 25-year-old woman presents with a high-grade fever of 101.1°F (38.4°C) and complaints of dysuria. She has a previous history of spontaneous vaginal delivery 4 days ago. Her labor was uneventful and she was discharged on 2nd day after her delivery. On per abdominal examination, her uterus is well contracted at 18 weeks-size. On vaginal examination, normal-looking lochia is seen and an intact episiotomy scar is noted. Breast examination is normal. Which of the following is the first step in her management?