Jane, a 21-year-old female, was seen in the office 10 days ago and was diagnosed with perennial allergic rhinitis and sent home with instructions for increased fluids, decongestants, and nasal steroids. She returns today with worsened symptoms of malaise, low-grade fever, nasal discharge, cough that is worse at night, mouth breathing, early morning unilateral pain over sinuses, and congestion. Physical examination reveals thick purulent nasal discharge, postnasal discharge visible in the posterior pharynx, periorbital swelling, and tenderness of sinuses upon palpation. She is 36-weeks pregnant and allergic to penicillin. Of the following, what is the most appropriate antibiotic?