Fatigue is one of the most common side effects of radiation therapy. Patients are not restricted from normal activity during radiation therapy; however, they should balance normal activity with periods of rest. Fatigue is typically more severe 2-4 hours after treatment.
Amoxicillin remains the drug of choice for acute, uncomplicated bacterial sinusitis. Amoxicillin is most effective when given frequently enough to sustain adequate levels in the infected tissue. While often prescribed twice daily, it is even more effective if taken in 3 or 4 divided doses.
Sinus infection : It sounds like you have a sinus infection. Flonase will not be enough. You need an antibiotic that is very effective for the sinus like Augmentin (amoxicillin and clavulanate) 875mg two times a day for 2 weeks. You also need an sinus decongestant like claritin-d 12 hour also twice a day.