my 2 month old son has lots of mucus/flem

Hello, my two month old son has had mucus/flem in his throat and nose since he has been born. there are days he has no issues, and there are days like last night where he is constantly choking and coughing on it. I have tried saline solution to thin it out and suck it out, but it only takes out a tiny bit. He suffers with this every day, and the poor thing cant sleep cause it it always waking him up. I have talked to the doctor several times and they only tell me to give the saline or to let it go away on its own.  Since he was born at 34 week, because he is a preemie, no medications can be given. All they tell me its the way it is and there is nothing you can do. But i know there has to be something. Its gets so bad and it breaks my heart when he cant breathe right and he cant sleep. All i hear is this constant gurgerling. Any ideas on what i can give him that is safe and non-harmful?