Hi
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Since this itch comes before your periods only, this could be related to lowering of estrogen and higher progesterone. Please consult a gynecologist and try and assess this. It can also be due to a disturbance in normal vaginal bacteria just before periods. Lactobacillus preparations or estrogen creams may help. However, since vagina is a sensitive area, please do not try these without medical prescription.
Take care!