The pollen in spring gives me terrible stuffiness, which is very uncomfortable.

stuffiness 是形容词 stuffy 的名词形式。stuffy 由 stuff（东西、材料）加后缀 -y 构成，本义是"充满东西的"，引申为"不通气的、闷热的"。stuffiness 指"不通气、闷塞"的状态，在这里特指鼻塞的感觉。