3 year old has been congested for 6+ weeks

My son recently turned three and had a cold with congestion and mucus. I think it’s possible he had back to back colds, but he is still congested now more than six weeks later which isn’t normal for him. He doesn’t have a fever, hes not coughing, he’s eating, drinking, playing and sleeping normally. Some mornings he has some mucus that starts to come out and we use a snot sucker to get it. He doesn’t know how to blow his nose yet, unfortunately. Then the rest of the day he won’t have any actual mucus or snot coming out but he is still breathing out of his mouth. Some mornings there’s nothing.

We took him to the pediatrician a few weeks ago and she didn’t seem concerned. Said his ears are clear, lungs were clear and he was happy and acting normally. I followed up with the office again and they still didn’t seem concerned but said I could bring him back which I am planning to.

He is not in daycare but does see some toddler friends on weekends etc. We have tried the neil med saline rinses for several days in a row, didn’t seem to help for more than immediately after so we stopped bc he hated it. He is on allergy medicine 2.5ml every night for seasonal allergies that started in the spring. He can somewhat breathe through his nose at night after he tries for a bit it seems to clear a little. I also started giving him probiotics geared toward ear/nose/throat health. Pediatrician also didn’t think it was a sinus infection because he’s not in pain and doesn’t have mucus the bulk of the day.

I just don’t know what else to do. I am taking him back to the ped and will see about an ENT appointment if needed but it’s just so strange he has never had congestion this long before.

If anyone has other ideas or things to check for I’d love to hear it. Thank you!