Itching of the pubic hair that worsens at night should be considered to be caused by pubic lice.
The first thing to look for is to see if there are any insects or eggs attached to the pubic hair.
If not, pay attention to the local cleanliness of the vulva, wash with warm running water and try to wear cotton underwear and loose fitting trousers.
If adult worms or eggs are found or if symptoms are not relieved, you need to visit a hospital for examination and follow medical advice on medication after the diagnosis is clear.