I Gets Red Rash With So Much Itch On My Back When I Go Outside The Home. What Can I Do ?

when i go outside the home, in the sun, a red rashes were appeared on my back. it was the first time that i have problem like this. i am a player, i play volleyball all the day, but now a days, when i start playing volleyball, problem will occur, just within a minute. even at the time when doing work. i am very sad, from last 2 weeks i m not going to college because of this problem, please help me.