Sun rash or usually appears after minutes exposure to the sun and can be extremely itchy. This is common in children and young women and tends to be recurrent. It is important to have a sunscreen with a high SPF to prevent this from occurring. You may try over- the-counter anti-histamine medications to provide relief for the itching or stronger prescription medications from your doctor. Try to avoid direct exposure to sunlight especially during midday where it is the strongest.
Take care and regards.