A 29-year-old non-smoker man presents with sneezing, post-nasal drip, eye-watering, and an itch of his posterior pharynx. These symptoms tend to be worse in the spring and summer and have been bothering him since mid-April, about 1 month ago. His past medical history is remarkable only for mild asthma induced by being outdoors. He takes no regular medications but does take diphenhydramine on occasion. Most appropriate diagnostic test at this time is?