Otitis Externa: This is the most likely diagnosis given the location of the pain (outer ear) and the history of allergy to penicillin (Travis pcn allergy), which may limit treatment options but doesn't directly influence the diagnosis. Otitis externa, also known as swimmer's ear, is an inflammation of the outer ear and ear canal, often caused by infection.

Allergic Reaction: Given the patient's allergy history, an allergic reaction could cause outer ear pain, especially if the patient has been exposed to an allergen.
Eczema/Dermatitis: Eczema or dermatitis of the outer ear can cause pain and discomfort, and could be related to or exacerbated by allergies.
Furuncle/Carbuncle: A furuncle (boil) or carbuncle (cluster of boils) on the outer ear can cause significant pain and may be related to bacterial infection, which could be a concern given the patient's allergy to penicillin.

Malignant Otitis Externa: Although rare, this condition is a severe infection of the outer ear and skull cartilage that can be life-threatening, especially in diabetic or immunocompromised patients. It requires prompt diagnosis and treatment.
Necrotizing Otitis Externa: A severe form of otitis externa that can lead to significant tissue damage and has a high morbidity rate if not treated aggressively.
Temporal Bone Osteomyelitis: An infection of the bone in the skull that could spread from the outer ear, potentially leading to serious complications.

Relapsing Polychondritis: A rare autoimmune disorder that can cause cartilage inflammation, including in the ears, leading to pain and deformity.
Sarcoidosis: A condition that can cause inflammation in various parts of the body, including the ears, though ear involvement is rare.
Erythromelalgia: A disorder characterized by burning pain, heat, and redness in the hands and feet, but can rarely affect the ears, causing similar symptoms.