Every night after 6pm my eyes feel irritated. Mid to late day there is yellowish goop at the tear duct and lid margins get redder. Why just at night?

Irritated eyes that. You describe can be caused by a lack of tears or ocular inflammation. The addition of yellow mucous discharge and lid margin inflammation can also be indicative of a blepharitis. In general, a response to either ocular allergies or lid margin disease should be focused on first. A slit lamp exam by your ophthalmologist can diagnose the exact cause and rx the best ocular drop to treat your condition.