Viral conjunctivitis: This condition is characterized by inflammation of the conjunctiva, often accompanied by symptoms such as redness, itching, and discharge. The presence of headache and fever could be indicative of a viral etiology, and viral conjunctivitis is a common condition that fits these symptoms.

Sinusitis: Given the proximity of the sinuses to the eyes and the fact that sinus infections can cause referred pain to the eyes, sinusitis is a plausible diagnosis. Headache and fever are common symptoms of sinusitis, making it a likely consideration.
Migraine with ocular involvement: Migraines can cause severe headaches and, in some cases, can involve the eyes, leading to pain and sensitivity. While fever is not typically a symptom of migraines, it could be coincidental or related to another condition.
Dry eye syndrome: Although less likely to cause fever, dry eye syndrome can lead to significant eye pain and discomfort. If the condition is severe or if there's an associated infection, it might explain the headache and fever.

Endophthalmitis: This is a severe, sight-threatening infection within the eye. Although less common, it's crucial to consider due to its potential for serious consequences, including vision loss. Symptoms can include severe eye pain, vision changes, and systemic signs like fever.
Acute angle-closure glaucoma: This is an ophthalmic emergency characterized by sudden, severe eye pain, headache, and vision changes, often accompanied by nausea and vomiting. Fever might not be a primary symptom, but the condition's urgency warrants its inclusion in the differential diagnosis.
Orbital cellulitis: An infection of the tissues surrounding the eye, orbital cellulitis can cause pain, swelling, and fever. It's a serious condition that requires prompt treatment to prevent complications.

Syphilis (secondary): In its secondary stage, syphilis can cause a wide range of symptoms, including eye pain and headache. While rare, syphilis is a great mimic and should be considered, especially in patients with risk factors.
Temporal arteritis (giant cell arteritis): This condition involves inflammation of the blood vessels and can cause headache, jaw pain, and visual disturbances, including eye pain. Fever might be present, and while it's more common in older adults, it's a diagnosis that should not be overlooked due to its potential for causing blindness.
Cavernous sinus thrombosis: A rare but potentially life-threatening condition, cavernous sinus thrombosis can cause headache, fever, and eye pain due to the formation of a blood clot in the cavernous sinus. It often arises as a complication of facial or sinus infections.