Chronic Rhinosinusitis is itself a cause of Allergic Pharyngitis... So its not a loss to do a CT nose and PNS...  You can get a fibreoptic laryngoscopy done simultaneously to evaluate your throat

First we need ur chief complaints in detail to knw exactly what ur problem is. Assuming that u have pharyngitis no need of CT PNS . pharynx can be directly examind by naked eye and VIDEO LARYNGOSCOPY for deeper vision. if there is any change in voice that requires VLS . if pharynx and esophagus hav to be seen UPPER GASTRO INTESTINAL ENDOSCOPY has to be done. so investigations depend on ur complaints which need to be known