Took my baby to A and E when he was congested , he was given saline drops for the nose that helps moisten the snot which then runs out on its own . I also put drops of Olbas on his cloths during night time , so he can sniff it in . He’s much better now and no longer congested . If he’s not eating , maybe contact Gp again.
Tummy time really helped bring the congestion out for mine, need to do the saline spray and snot sucker after. Vapour bubble bath too
I'm assuming the GP listened to his chest? Mine had the same and it did progress to bronchiolitis and she was admitted and had to have an Ng tube. If she's getting worse or not improving I'd defo go back to the GP. Unfortunately their colds/congestion do take ages to fully recover (mines still coughing and slightly congested now) but for your own peace of mind worth getting them to regularly check x
Have you tried snuffle babe, they do like a vapour rub for babies and drops for their nose. We also use a calpol vapour plug in. Not sure which thing worked for her but something definitely did