Just had to reply to your question about prickly heat. I have suffered so very badly with this over the years. Absolutely dreaded going out in the heat for fear of this coming on. I have before now had to sit in a bath of cold water just to feel better and one evening had to leave a restaurant as I couldn't bear the itching/pain any longer. I was unable to bear any clothes on me! I usually come up in a huge ugly red rash on my neck, chest, back and arms. I have cried with the awful itching and felt so self conscious having to cover up and not being able to wear summer vest tops etc. Looking around I seemed to be the only one who ever suffered, seemed so very unfair!
I have now found some relief though and it requires some preparation. Last year prior to my holiday, I took 1mg of Prednisolone daily for 2 weeks prior to me going away and during the holiday, (as it happens I am now on 5mg daily mainenance dose anyway so that takes care of that!). I also took 15mg of beta carotene daily. I had about 6 sun bed sessions to prepare my skin (despite the recent scares) and never sunbathed in direct heat. Everytime I felt too hot, I either went into the swimming pool, took a shower or sprayed myself with a water spray. I also used Boots clear Soltan suncare spray which I found very good as it is light and doesn't clog the pores.. after all it is the sweat glands being blocked that causes prickly heat, so try not to sweat either!!
Obviously this advice is for when you are on holiday. I find if I tend to avoid the sun otherwise, stay in the shade and try as much as possible simply not to get too hot. Little battery fans that you can carry around in your handbag are good. I do hope this helps, as I can really sympathise with you.