My cat, for the last few years, has been sneezing constantly. She gets antibiotic shots...

Sneezing is usually a sign of nasal irritation. Nasal irritation can be due to allergies, infection, foreign bodies in the nasal sinus and tumors. In some cases a radiograph of the head and nasal sinuses may help determine what is going one. In other situations the cat may need an endoscopic examination of the nasal passage to further diagnose the problem.



Source: http://www.purinaone.com