I'd take him to the vet, or at least call and see what they say - sounds like he has a sinus infection or other upper respiratory infection and he may need antibiotics. Or they may be able to recommend other medications (OTC or otherwise) that might be helpful and would be appropriate. And FYI - a nasal decongestant is NOT one of them - ALWAYS call your vet and check with them before giving your dog anything!
ETA: We are not "being jerks" by telling folks they need to bring the pet in - sometimes we just can't give advice over the phone without seeing the pet because we could be totally wrong and things could go from bad to worse. And where I work currently, it is the practice policy that receptionists and techs are not allowed to give advice over the phone without checking with a doctor first - it's just too much of a liability issue.