Lichen nitidus is a strong possibility.Calamine lotion helps.
I have looked at the photo of your itchy rash.
Looking very closely at the rash I can see a small area that has a small white line. Another cluster of small red spots also go in a straight line.
Although it appears as it could be an allergic reaction or possibly bite marks, having seen the little white line brings me to think that this is the scabies bug.
I would advise you to get the doctor or pharmacist examine your wrist to confirm the right diagnose.
It it is scabies you will need to get a special solution to apply on to your clean washed wrist. Your pharmacist may recommend a solution for you and what you need to do.
Lichen planus is the chronic variant and the lines represent koebnerization (Lesions along the lines of itch).
External application of steroid helps.
Do consult your doc.