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Perception of itching increases in the night as the patient is not doing anything but resting where as during the day, social obligations keep his/her mind away from the symptoms. This could be one reason for increased itching in the nights.Dry skin
can also cause severe itching
as there are more chances of contact irritation occurring in those areas.
Another cause could be pin worm infection
which causes increased itching in perianal and groin region during the night.
I suggest vaginal swab and perianal swab testing to rule out infection.
Get in touch with your GP for appropriate therapy after test results.
Personal hygiene in those areas is a must.