Dear moms ?, my little one has been having thick phlegm for two weeks …

Dear moms ?, my little one has been having thick phlegm for two weeks now, with no fever or cough. It's just so thick that even sucking it out is difficult. Can this be normal? Saliva also flows, and there are no behavioral changes. Even after sucking out the phlegm, it seems like nothing comes out anymore, but within a couple of minutes, there's a whistling sound in his nose when he breathes. Visually, there's nothing visible. I don't know what to do anymore. What should I do? The pediatrician said to clean the nose more often and to drip a physical solution. I'm doing all of that, but the humidity at home matches the standard measurements