What could be the cause of vaginal itching after hysterectomy?

Many possibilities: You can get vaginal itching for the same reasons as before your hysterectomy! for example, vaginitis (yeast or candida is very common), an allergic reaction to something you had contact with (like a cosmetic, soap, clothing dye, douche, etc), an infection with herpes, and other skin conditions.

Varies: The itching could be an allergic reaction, a yeast infection, or a part of the normal healing process after a hysterectomy.