You are evaluating a 48-year-old woman with headaches. She reports a long history of occasional sinus headaches, usually responding to over-the-counter treatment. Over the last several months, the headaches are occurring more frequently, and are actually more painful than they have been in the past. Over-the-counter medications, effective in the past, no longer work. What is the most appropriate next step?

A Use antibiotics to treat sinusitis and follow up if no improvement B Use prescription antihistamines and follow up if no improvement C Use prescription decongestants and follow up if no improvement D Obtain radiological imaging of the brain