The most appropriate next step in management is a methacholine challenge test. Testing will confirm the degree to which this patient's symptoms are caused by hyperreactivity of the lungs. The frequency and degree of this patient's symptoms are concerning, and he has several risk factors and clinical factors (such as a history of allergies, cough without exercise, and symptoms occurring several times a week) that suggest the possibility of asthma as the underlying diagnosis. Though some patients with asthma wheeze with exercise, it is not a necessary symptom to consider the diagnosis; exercise intolerance, breathlessness, and cough can be the primary symptoms as well. Because of the significant morbidity and mortality associated with undiagnosed and untreated asthma, further evaluation of this possibility is indicated in this patient. Because spirometry results are normal, which can occur in patients with asthma, further confirmatory testing with a bronchial challenge test (such as with methacholine) is warranted to further evaluate for possible asthma.

Managing only this patient's allergic rhinitis with a nasal glucocorticoid would not treat possible underlying asthma adequately to protect him from nighttime cough and shortness of breath during exercise. However, counseling avoidance of exercise in locations with allergens would be appropriate.

Although a therapeutic trial of an as-needed β₂-agonist inhaler may seem reasonable, a more extensive assessment and proper diagnosis of this patient's symptoms concerning for asthma will ensure that adequate medications are prescribed for chronic management.

In patients with asthma, spirometry results between episodes are often normal. Additionally, this patient is experiencing frequent and disruptive symptoms. Therefore, clinical observation without further evaluation would not be appropriate.