I'm 22 Years Old, I'm Allergic To Cold And Dust.

I'm 22 years old, I'm allergic to cold and dust. I consulted my doctor who prescribed me to take montek LC and fexofenadine for a month. I feel relieved after taking them during night time. When I stopped taking them after a month I got those allergies again. Should I continue the usage of montek LC and fexofenadine. If so is there any side effects for prolonged usage of those tablets?? . also, is there any other way to cure my allergy??.