I have similar symptoms, a rash on my neck that comes and goes. But I have started using new products that make my skin sensitive to the sun. I stopped using them. I have started to avoid sun exposure (wear a scarf) and use a higher SPF sunscreen. Maybe sun exposure? My mother had a reaction to cleaning supplies. We both have sensitive skin. In the past these things have also caused a reaction.....laundry detergents, perfume, husbands chin stubble. Hope this helps.
Hello,
From the symptoms, although it is difficult confirming a diagnosis without examination but it can be contact dermatitis. Take some antihistaminics like Benadryl or Claritin and apply some calamine lotion on the rash. If the symptoms persist then please get it evaluated from a dermatologist/ allergist as oral and topical steroids may be needed.
I sincerely hope it helps. Take care and please do keep me posted in case you’ve any additional doubts.