My daughter has glue ear, and what you are saying sounds familiar. We are currently debating whether to have grommets or not so would be interested to hear how you get on. How old is your ds? My dd is 4 and has just started school. We are waiting to see if the teacher thinks it's causing her problems.
The newborn hearing tests only test the nerve bit of the hearing, doesn't test the clarity of what is being heard DS2 passed after several attempts but had glue ear. He struggled with frequesnt ear infections & inflammation & had some fluctuating hearing loss. Ask your gp to refer you to ENT & audiology (depends on local set up).