Hello and welcome to e health forum.
First and foremost, you might consult with a doctor for a examination to rule conditions like allergies, insect bites, dermatitis, or parasitic infestations (Scabies).
In the mean time, you can avoid using very hot or cold water while bathing. Use of luke warm water can help reduce the symptoms.
You can also avoid the habit of scratching yourself, and apply cold packs to the affected area, to numb the sensation. Use of calamine lotion will also be very helpful.