What Causes All Over Body Itching Causing Small Bumps?

hey there doc. im a 17 year old boy with medical problem, it started this summer and it has effectively ruined most of my social life.

most of my body starts to itch (an almost burning feeling) everytime it gets just a little hot, I also develop small bumps at the itchy parts of my body (back, chest, tummy, inner and outer thighs, forearm and even sometimes my neck and scalp), this means that i cant be outside in the sun, no parties, no exercise and no intimate moments with my girlfriend, its all just too hot.

as i said, it started this year, i've never experienced it before.