unknown heat reaction

It started 6 months ago, where I used to get so itchy in the sun, that it felt like hundreds of needles poking me at the same time. One day that painful feeling went away, but it was replaced by a different feeling. for about 2 months now, whenever I get hot (whether sitting in the sun, doing pushups, cycling), my body reacts to the heat. I get very itchy, and spots appear only on chest. I sometimes get headaches and my breathing becomes very hard. It becomes hard for me to focus and even talk. My heart starts to race to the point where I cant stand anymore. My skin on my face and neck becomes pale and so thick that my pores close up. My face looks like an orange peel.  I should be sweating after excercise, but sweat doesn't come out. Only after sitting in a cool place for 20 minutes, will I start to sweat. Once i start sweating, it doesn't stop for more than 40 minutes.

I have been to doctors and allergists. they have not been able to diagnose me. they gave me antihistamines, but they don't help at all. My blood work came out normal. Doctors just tell me to stay indoors or in cool temperatures.

I am a professional golfer and I am out in the sun on average 8 hours a day. Staying indoors is NOT an option for me. Doctors, can you help me?