A 17-year-old woman presents with lower abdominal pain and vaginal discharge. She is sexually active with men with inconsistent barrier protection. Her temperature is 101°F. On examination, there is yellow cervical discharge, no cervical motion tenderness, however, uterine and left adnexal tenderness is present. An ultrasound does not show any evidence of tubo-ovarian abscess. A pregnancy test is negative. Which of the following is the most appropriate treatment for this patient’s condition?