Dog stuffy nose

My dog has been suffering from stuffy nose since two weeks ago. At first the discharge was watery ,which becomes thick later on. The discharge is clear. We've visited the pet and he has been given antibiotics and pseudoephedrine But no progress. The dog's nose is now kind of swollen inside. He also refuses to eat and only wants to drink. He will only eat a tiny bit occasionally.Any advice on what is wrong with my dog as the local vet diagnosed him with dog flu but it has been more than two weeks with no progress.Please help.