Periorbital Cellulitis: This condition is characterized by infection of the eyelid and surrounding tissues, often presenting with swelling, tenderness, and pain, especially when moving the eye. It's a common and relatively straightforward diagnosis that matches the symptoms provided.

Blepharitis: Inflammation of the eyelids can cause swelling, tenderness, and discomfort, including pain when moving the eyes. It's a common condition that can be associated with eye movement pain due to the inflammation of the eyelid margins.
Conjunctivitis: Although primarily an infection or inflammation of the conjunctiva, severe cases can cause significant discomfort, including pain on eye movement, along with swelling and tenderness of the lids.
Dacryocystitis: Infection or inflammation of the lacrimal sac can cause pain, swelling, and tenderness in the area of the eyelid, potentially worsening with eye movement due to the anatomical location.

Cavernous Sinus Thrombosis: A rare but potentially life-threatening condition that can present with periorbital swelling, pain on eye movement, and other neurological signs. It's crucial to consider this diagnosis due to its high morbidity and mortality if not promptly treated.
Orbital Cellulitis: Similar to periorbital cellulitis but involves the orbital tissues posterior to the orbital septum. It can cause more severe symptoms, including significant pain on eye movement, proptosis, and vision changes, requiring urgent medical attention.
Herpes Zoster Ophthalmicus: Shingles affecting the eye can cause severe pain, swelling, and potentially lead to complications like uveitis or glaucoma. The pain can precede the rash, making early diagnosis critical.

Wegener's Granulomatosis (Granulomatosis with Polyangiitis): A systemic vasculitis that can affect various parts of the body, including the eyes, causing a range of symptoms from conjunctivitis to orbital inflammation.
Sarcoidosis: A condition that can cause inflammation in various parts of the body, including the eyes. Ocular sarcoidosis can present with uveitis, conjunctivitis, or lacrimal gland inflammation, potentially causing the symptoms described.
Thyroid Ophthalmopathy: Associated with Graves' disease, this condition can cause swelling of the tissues around the eye, including the eyelids, and can lead to pain on eye movement due to the increased volume of the orbital contents.