Post Menopausal. Over Weight. Why Is There Blisters And Perfume Irritation?

I am a white British woman, 58, post-menopausal, somewhat overweight but otherwise generally in good health. A few weeks ago the front of my neck started itching in the crease under my chin. I stopped using perfume in case it was irritating the skin. I have just been on holiday, we had a couple of days of temperatures in the 30s. I used Factor 30 and 50 sunscreen on my neck and chest becuase I know I burn easily there, I have fair skin. I didn t get sunburned, but the side of my neck began to be more and more itchy as the days went by, with a cluster of raised spots like little blisters or skin tags . Now I am home, the rash has gradually spread from my neck to my upper chest, between and under my breasts, and is continuing to spread across the top of my stomach. My genital area has also begun to itch in the last day or so. Wearing a bra is uncomfortable, and the rash and discomfort is getting worse day by day. I haven t changed soaps, perfume, detergents or medications recently. I had scabies a couple a years ago but this is different, what could it be? And, more to the point, what can I do to make it go away?