What Can I Do About An Infant Having Persistent Mucus, Nasal Congestion, And Excessive Saliva Causing Difficulty In Breathing?

My boy is 3months alreadybut he is beeb struggling with mucus since. He struggles to breath because it stuck in his throat sometimes n his nose get blocked most of the time. N theres too mush saliva that makes bubbles or i can they look sleepery. What can i do