I am really worried the eye may need to be removed, so get that
dog to a vet today. All that swelling from
infection behind the
eye can also cause meningitis which can be fatal, so there is no time to lose.
A similar incident happened to a neighbor's dog several years ago, and the eye had to be removed because the infection could have blinded the other eye by traveling along the optic nerve. The dog did just fine after surgery.