It could be a sign of prementrual hormonal changes or fungal infection. It could also be an allergy if you have changed your soap or use any gels for intimate hygiene.
At times even a irritation caused by entangled hair of pubes can also cause itching. Avoid shaving. Try trimming
Next Steps
Only a proper examination from a gynecologist can help to diagnose the cause and the treatment. so meet a nearby gynecologist and get evaluated.
Health Tips
In young persons many times, excessive vaginal normal discharge due to ovulation or before menses can also cause itching. It could also be a sign of arousal. The gynec examinaiton will rule out any infections or local swelling or other causes.