Herpes Simplex Virus (HSV) infection: This is the most likely diagnosis due to the presence of a vulvar ulcer and a vesicular rash, which are characteristic symptoms of genital herpes. HSV infection is a common sexually transmitted infection that can cause painful ulcers and vesicles in the genital area.

Syphilis: The primary stage of syphilis can present with a single, painless ulcer (chancre) in the genital area, which could be accompanied by a vesicular rash. Although less common than HSV, syphilis is another sexually transmitted infection that should be considered.
Varicella-Zoster Virus (VZV) infection: Reactivation of VZV can cause herpes zoster (shingles) in the genital area, leading to a vesicular rash and potentially ulcers. This diagnosis is more likely in individuals with a history of chickenpox or shingles.
Autoimmune disorders (e.g., Behçet's disease, pemphigus): Certain autoimmune conditions can cause ulcers and vesicles in the genital area, although these are less common than infectious causes.

Squamous cell carcinoma: Although rare, vulvar cancer can present with ulcers and should not be missed. A biopsy would be necessary to confirm this diagnosis.
Lymphogranuloma venereum (LGV): This sexually transmitted infection can cause ulcers, lymphadenopathy, and other systemic symptoms. LGV is less common but can have serious consequences if left untreated.
Granuloma inguinale (donovanosis): A rare sexually transmitted infection that can cause genital ulcers, which can be painful and bleed easily.

Vulvar aphthous ulcers: These are rare, painful ulcers that can occur in the vulvar area without an identifiable cause.
Vulvar Crohn's disease: A rare manifestation of Crohn's disease that can cause ulcers and fistulas in the genital area.
Vulvar ulcers due to other infections (e.g., chancroid, amoebiasis): These infections are rare in many parts of the world but can cause genital ulcers and should be considered in individuals with a history of travel or exposure to endemic areas.