What effect does long term use of Claritin nasal spray have on the body..?

In particular the sinuses, and nasal cavities. What is the rebound effect and is it permanent? I have been using this product for several years to treat my allergies and hay fever. I first began using it when my Doctor suggested it to me, and just never stopped. The strange thing is that my symptoms have gradually gotten worse over time, and now when I discontinue using the spray I become severely congested; to the point where no air can p through my nose...