According to information given by you, your dog might be having cold or flu. Cold or common flue in dogs is not just like humans. Symptoms like runny nose, coughing, sneezing, etc in dogs are due to upper respiratory tract infection that can be caused by bacteria or virus. Canine advenovirus type-2, Parainfluenza virus, and canine distemper virus are most common pathogen of cold like symptoms in dogs. Runny nose is also caused by Kennel cough in dogs. As many types of infections can cause common dold like symptoms in dogs, that is why differential diagnosis is required for proper treatment. So, it will be better to take your dog to vet.