Take him to the vet now. Birds naturally mask their symptoms when they are ill for as long as they can. When an uneducated owner who doesn't know what to look for in a sick bird realizes something is wrong, often times it is too late because the bird has been hiding his illness for a while. There should never be feces stuck to the birds vent or feathers. Until you can get to the vet, make sure the bird is warm. If his feathers are fluffed up this is a sign he is cold/sick. What color are his feet and are they cold? This is another thing to look for. I would suggest a low watt heat bulb placed over his cage to keep him warm until he sees a vet.
