Cellulitis: This is the most likely diagnosis given the symptoms of pain, swelling, irritation, and clear drainage in the affected area. Cellulitis is a common bacterial skin infection that can occur after an insect or spider bite, and its presentation matches the patient's symptoms.

Insect Bite Reaction: An allergic reaction to an insect bite could cause similar symptoms, including swelling, pain, and irritation. The clear drainage might be part of the body's response to the allergen.
Spider Bite (e.g., Brown Recluse): Certain spider bites, like those from the Brown Recluse spider, can cause necrotic lesions and symptoms similar to what the patient is experiencing, although the presence of clear drainage might be less typical.
Folliculitis: An infection of the hair follicles could be triggered by the bite, leading to inflammation, pain, and possibly some discharge.

Necrotizing Fasciitis: Although rare, this is a life-threatening condition that can arise from a bacterial infection following a bite. Symptoms can include severe pain, swelling, and possibly discharge, making it crucial not to miss this diagnosis.
Gas Gangrene: Another severe infection that could potentially follow a bite, characterized by rapid progression of symptoms including pain, swelling, and possibly a foul odor or discharge.

Erythema Migrans (Lyme Disease): If the bite was from a tick, there's a possibility of Lyme disease, which can present with a characteristic "bull's-eye" rash, although this is less common in the initial stages.
Leishmaniasis: In endemic areas, a bite from an infected sandfly could lead to Leishmaniasis, which can cause skin lesions and other systemic symptoms, though this would be highly dependent on the patient's travel history.