Allergic Conjunctivitis: This is the most likely diagnosis given the patient's symptoms of red, swollen eyes, itchiness, and minimal relief with Benadryl. The presence of drainage and dryness also supports this diagnosis, as allergic conjunctivitis often presents with these symptoms.

Viral Conjunctivitis: The patient's symptoms of redness, swelling, and drainage could also be consistent with viral conjunctivitis. The lack of significant relief with Benadryl and the presence of light sensitivity also support this diagnosis.
Blepharitis: The patient's complaint of itchiness in the eyebrow area and dryness could be indicative of blepharitis, an inflammation of the eyelids.
Dry Eye Syndrome: The patient's report of dry eyes could be a primary symptom of dry eye syndrome, which can also cause redness and irritation.

Acute Angle-Closure Glaucoma: Although less likely, this diagnosis is critical to rule out due to its potential for severe vision loss. The patient's symptoms of light sensitivity and headache could be indicative of this condition.
Keratitis: An infection of the cornea, keratitis can present with redness, swelling, and light sensitivity. It is essential to consider this diagnosis to prevent potential vision loss.
Orbital Cellulitis: This is a serious infection of the tissues surrounding the eye, which can cause redness, swelling, and pain. Although less likely, it is crucial to rule out due to its potential for severe complications.

Sjögren's Syndrome: An autoimmune disorder that can cause dry eyes and other systemic symptoms. Although rare, it could be considered if other diagnoses are ruled out and the patient has a history of autoimmune disorders.
Thyroid-Associated Orbitopathy: A condition associated with thyroid disease, which can cause swelling and redness of the eyes. This diagnosis would be considered if the patient has a history of thyroid disease or other suggestive symptoms.