I've had a dog for 15 years now, what kind is he?!?

So I've had this little dog for forever it seems now he's still alive but because of his age i think we're going to lose him... I want to know what he is. He is little (between chihuahua and cocker) and black with a white chest. his ears aren't exactly small but they are definitely not as long as a cocker spaniel's ears. Some sort of mutt we've decided, but of what? We have for the most part decided he's chihuahua and doxin mix, but what else? I'll put up pictures in a few if it helps... thanks!