If it's fungus, antibiotics won't help and might weaken him more, you need to look for something specifically antifungal. Keep in mind this still doesn't take dosage into account. (I'm guessing it might be fungal because one symptom is patchy shedding like yours has. See: http://www.petmd.com/reptile/conditi...ytridiomycosis
High humidity isn't bad, but you might want to make sure it gets lower than that occasionally, make sure there's good ventilation.