Huge sympathies here.
I developed PLE a few years ago & ditto comments above to manage the situation. At first I thought it was prickly heat but the rash is triggered by sun exposure & follows a consistent pattern.
However, for now.
Don’t scratch. Certainly not with your nails.
If you need the relief of a scratch, try covering the itchy area with a clean towel & running the knuckles of your fist over it. You satisfy the urge to itch without scratching the skin. Taking oral anti-histamine will really help with the itching.
Anti-histamines - I find Loratadine once-a-day good enough & Boots own brand is often on offer in the summer months. Don’t hesitate to ask your GP (yes, show pictures) to prescribe something stronger if the standard Loratadine dose is not strong enough. I now take it through the summer months for nasal allergies AND as a preventative for PLE.
Avoid direct sunlight on areas of your body that are affected. For me its my legs. I have gone from bare legged summers of yore to minimal exposure & slathered in SPF 30 before baring my legs otherwise the rash comes up with a vengeance. If I miss a bit when I put the cream on, the rash will appear there so I now carry a handbag size tube of SPF50 cream in case I cannot find shade. This seemed excessive at first - more junk to cart about - but avoiding the allergic reaction is well worth it.
Avoid skin products with PABA & perfume in ingredients. Good quality hypo-allergenic skin products will not have these ingredients but check the contents every time you buy them.
Wear loose light natural fabrics so your skin can breathe & wash with non-bio detergents. Fairy & Persil non-bios are the go-tos on the supermarket shelf.
Aloe Vera gel is good for calming the worst of the raging prickling, you can slap it on as much & as often as you need.