agree with others that this sounds allergic. as noted above prick test only tests a limited number of antigens so isn't dispositive re allergies.

i also have the sinus congestion thing, year-round, much worse on one side. Regular neti pot (2X day) and humidifier use in BR help a lot. I also use flonase type spray during seasonal allergy peaks (right now) and have had good results w/ that. but if the claritin works, why not keep on with that?