Bartholin's cyst: This is the most likely diagnosis due to the location (one side of the labia majora) and description (fluid-filled bumps) of the symptoms. Bartholin's cysts occur when the Bartholin's gland, located on each side of the vaginal opening, becomes blocked, causing a fluid-filled cyst to form.

Folliculitis: An inflammation of the hair follicles, which can cause bumps or pus-filled spots on the skin, including the labia majora.
Sebaceous cyst: A benign, fluid-filled cyst that can occur on the labia majora, although less common than Bartholin's cyst in this specific location.
Vulvar abscess: A collection of pus in the vulvar area, which can cause a painful, fluid-filled bump.

Malignancy (e.g., vulvar cancer): Although rare, any unusual or persistent lump in the genital area should be evaluated for the possibility of cancer to ensure early detection and treatment.
Herpes simplex virus (HSV) infection: Can cause painful, fluid-filled blisters in the genital area, including the labia majora.
Syphilis: A sexually transmitted infection that can cause a variety of symptoms, including painless sores or bumps in the genital area.

Hydrocele of the labia majora: A rare condition where fluid accumulates in the labia majora, similar to a hydrocele in the testicles.
Vulvar hidradenoma: A rare, benign tumor of the sweat glands that can occur in the vulvar area, including the labia majora.
Lymphangioma: A rare, benign growth of the lymphatic vessels that can cause fluid-filled bumps or lesions in various parts of the body, including the genital area.