Cold Sore (Herpes Simplex Virus): This is the most likely diagnosis due to the description of painful, red-colored pimples near the lips. Cold sores are a common condition caused by the herpes simplex virus, characterized by small, fluid-filled blisters that are painful and typically appear around the mouth.

Acne: Although less common around the lips, acne can cause red, painful pimples. However, the location and description might lean more towards other diagnoses.
Impetigo: A bacterial infection that can cause red sores on the face, including around the mouth. It's contagious and can be painful.
Perioral Dermatitis: A skin condition characterized by a rash around the mouth, which can include red bumps or pimples. It can be itchy or painful.

Erythema Multiforme: A skin condition that can be triggered by infections (including herpes simplex) or medications, characterized by target-shaped lesions. It can be severe and requires prompt medical attention.
Cellulitis: A bacterial skin infection that can cause redness, swelling, and pain. If it involves the face, it can be particularly dangerous due to the risk of spreading to the brain or eyes.
Lupus: Systemic lupus erythematosus can cause a butterfly-shaped rash across the cheeks and nose, which might initially be mistaken for pimples. It's an autoimmune disease that can affect various parts of the body.

Sarcoidosis: A condition that can cause skin lesions, including around the mouth, though it's less common. It's characterized by the growth of granulomas (inflammatory cells) in different parts of the body.
Keratoacanthoma: A rare skin growth that can resemble a pimple but grows quickly. It's usually found on sun-exposed areas but can appear near the mouth.
Basal Cell Carcinoma: A type of skin cancer that can initially appear as a small, red bump. Though rare in the description given, any new or changing skin lesion should be evaluated for the possibility of skin cancer.